That's so sad :(
I had a few penpals as a kid. Mostly people I met in summer camp I think. Those lasted a few years each I think but over time we all lost interest. Especially since the world was changing and the Internet and email and phones became a thing. But, one, just one of them is still my friend to this day
Though we don't exchange letters anymore and now chat on social media.

Then, like 7 years ago or so I randomly got another pen pal. We write very infrequently but still write each other