Aside from what you said about far away/not easily accessible countries or adresses in other alphabets… well, postcards are small pieces of paper, after all.
They can get irreplacable damaged and some times they just… fly away and get lost forever (I suggest reading about “Ambulance covers” or looking about that on youtube, I think Explore Stamps has a topic about that).
HOWEVER. Sometimes the system works, it is just the slowest of the snails. And the postcards that we lost in a fairly easy route found they way home many, many months later.
To put an example on something that happen to me months ago:
I sent a postcard to my aunt and her family. My aunt lives ten minutes driving from whre I live, in the big city next to my smaller town that takes 15 min to reach by public transport. Same area, same postal system… You get the idea.
I sent it in July, it should have taken a week… IT ARRIVED IN OCTOBER!!!
It would have taken me half an hour to walk there and hand deliver it myself!
It got lost along the way in the system and it ended up with a pretty cool cancellation, I wrote a post here [Triple inverted]
My point is… postcards that expire are marked as so after just 60 days. If postcrossing teaches you anything, is to be patient and never loose faith!
And yes, it is frustrating when a card that you so thoughtfully loved never reaches destination, but hey, that’s why we have emails, phone calls and even video-calls, so the actually important messages never get lost again.
I hope you card finds its way home, eventually.