When I was in high school and university decades ago, before social media and even stable phone numbers, friends used to come and go all the time; co-workers at summer and co-op jobs, classmates, roommates, ...
You'd have beers and a few good times and then the next term/year would happen and you might never see them again. It didn't feel like rejection because there really wasn't a practical way to stay in touch. You only felt rejected by romantic partners and old friends who decided to move on.
Now, we "connect" to everyone; we follow each other on Facebook/Twitter/Signal/WeChat and we have each others emails.
I'm trying to imagine the roommates I had one summer, who I had almost nothing in common with but who shared their stash with me because I would bring good steaks and fresh vegetables from home, reaching out to me a year later and saying "hey man, why did you ghost us?". What would you even say to that?
So, now, when these temporary friendships are over ... we have this lingering connection that doesn't just go away at the end of term. Someone has to take the extra step of closure.
I get that this feels like rejection but that feeling is a new thing.
Summer loves and friendships were meant to end with a sobbing farewell at the end of August, not with a unfollow and block in November.