The most understandable answer I can think of is that people don’t speak English very well.
Otherwise, some people just might think the postcard itself is more important than the message on it.
Sometimes when I read a person’s profile it becomes apparent that they sent the postcard like this for reasons such as these.
Of course, there might be other reasons, like people not caring too much about writing a lot. (One time I received a postcard with only a pre-prepared sticker with happy postcrossing on it where I got that impression.)
But generally, if people don’t write a lot it might also be because they want to put a postcard full of stamps or decorations.
For example, I’ve received wonderful postcards with many stamps on them, but not a lot of text.
When I myself get a profile that doesn’t speak English, I’ll generally make a drawing on the postcard and use google translate to translate a short greeting to a language they speak. (I don’t trust google translate enough to translate a whole message.)
I agree with the others above that it may be a language issue or maybe they don’t like writing in general. I figure if it says “Happy Postcrossing”, at least they tried. I’ve gotten postcards before where it was just my address, the postcard ID and nothing else, not even drawings, stickers, or other decorations.
Who knows what goes on people’s head when they do that?! Probably tons of different reasons. Unless people who just write “Happy Postcrossing!” come here and answer the question, all we can do is guess.
I recently received 3 blank cards in an envelope for an official card, with a few words on the envelope.
I thought, “well, that’s a bit odd”. When I registered it, the man explained that arthritis made it hard for him to write, but he still wanted to participate as he got rid of his existing inventory of cards.
I appreciated that he explained in his profile, and it helps me to understand that perhaps writing is painful for some people but they still want to connect.
That’s interesting. I’ve never gotten an explanation for any of the blank cards I’ve gotten. Usually if people have a physical disability, what they’ve done is to type a message instead of handwriting it. But I guess typing or even putting on stickers might be difficult for some people, too.
Here’s a topic where people suggest just writing Happy Postcrossing for a profile which the sender finds rather confrontational.
I’ve seen that topic. But if that becomes the norm, then one will wonder if a “Happy Postcrossing” means that the sender just doesn’t like your profile. Which is fine, I suppose. There are all sorts of different people in the world and I’m sure there are people who will immediately rub each other the wrong way no matter what.
I almost added that I didn’t mean to imply that the OP of this thread received Happy Postcrossing messages for this reason. Just some interesting context for the bigger conversation.
Some people also find it weird to write a lot on a card so maybe it didn’t occurr to them…
Like when postcards were a quick greeting from your holiday, I still wrote a lot but my mum says “back in her day” you’d just write a quick hello and that’s it (she saw me write a postcard to a postcrossing friend and she was like 
at how I filled every space).
But yes, I get a bit ‘meh’ about cards which don’t say much but I try to think we are all different, if the card is nice and they are friendly enough even in a few words (I never got a ‘happy postcrossing’ alone, though I got things like ‘hello from X’. And that could also be they don’t speak a lot of English).
Personally, I love to write and fill my postcards and my snail mails with paragraphs.
When I joined (and sometimes still), I read often in profiles “please write also something else than Happy Postcrossing” and also read some threads that mentioned this. But, I’ve noticed it’s not at all so common as you think it might be when reading the topics about this.
Out of my over 2400 received cards, I can say for sure, that one had only this text.
Might be more. But so few, I don’t remember.
Maybe it was more common in the beginning of Postcrossing?
Or, there is one or few profiles who bulk send and don’t write anything else, and when many of the receivers write about this, it seems like there are more this type senders.
Also, all the above mentioned reasons.
I have written only once that, but then I write it “prettily”, it was to a person who’s other profile I got earlier, and she didn’t like anything about me 
so I didn’t want to write anything, but she liked that Happy Postcorssing card 
.
One never knows what struggles people might be having, especially in these pandemic times. If all they can manage is “Happy Postcrossing”, I take it as a smile from a stranger who wishes me well. It brightens my day and I move on.
Every card received is a little gift. 
Omg I received the same thing and can only assume from the same postcrosser!
maybe sometimes they are not good with english, or they don’t enjoy/can’t write much but still enjoy the exchange feeling.
In my experience it is often users from Asia or Russia who do just write Happy Postcrossing. I assume it might be a language problem?
Sometimes I get postcards written in the senders native language. Not sure if I like that better than just Happy Postcrossing
Yes, writing a lot on cards is probably a recent phenomenon. The stereotypical greeting would be “Weather is beautiful, wish you were here” which of course led to “The Weather Is Here, Wish You Were Beautiful”.
I always feel like these people don’t care, they are just mass producing cards with no thought whatsoever. Maybe they collect cards or stamps and don’t care about the text at all. Maybe they don’t even look at the profile because they don’t care about you, they print the IDs and addresses, glue them randomly on a stack of cards and drop them in the box. Perhaps they only care about receiving cards and are building up their numbers with the least effort. A new user wouldn’t know to say it so I know it is not them.
To me these cards are just trash. I donate the stamps and bin the rest.
There’s always something! I ask a question in my profile to help these people. I would happily take a card that just says I like carrot cake on it, even if that is a rubbish cake…
That’s what i do as well, i habe each month 1 questions for someone who looks on my profile where Ím curious about 
I hope that helps as i love to receive cards with a lot of text haha
We are all human. And none of us made of stone (even if it’s a very cheerful stone with lots of things to tell). We all have good days and bad days. And many of us sometimes don’t feel like to say/write anything using words, but still feel the need to say something with a card at least.
Even those who seem to be hunting for cards and stamps only, building up numbers and not giving us life novels or avoiding our endlessly random questions, even they do make an essential for Postcrossing effort of sending a postcard. And it’s worth something too.
I wouldn’t think of such card as trash. Normally I just say thank you, add a few words about the things I liked about the card and move on to sending cards and telling silly facts about me to other people. 