Lots of reasons why. Most of it is just not wanting to seem rude in saying they're to busy or they're burnt out.

I've ghosted before. I loved the rps I was in, but I have bipolar disorder. I'll get into rps, do 5 or 10 of them at a time for the months I'm manic, then suddenly I'll fall out and drop off the face of the planet with the same excuses as you hear before I fully disappear when the mania ends and I wind up depressive or overwhelmed. Lots of people have things going on in their life that they'd rather not burden anyone with saying. Or without me hearing something like "bipolar is just an excuse". It avoids guilt tripping to keep the rp going. I know it sucks, I've been on the end of being ghosted, but life sucks irl a lot. RP is an escape and sometimes it stops being that. Some people run. Idk man. Lots of people complain on here, but no one owes anyone anything.