The network effect is one reason, if users are responsible for the content then there will be a shortage of content until enough users join.
Beyond that, humans are social creatures and want to fit in. If your community mainly hangs out on one platform, people will want to be a part of that platform. What helps is if people with a large enough following or entire communities make the decision to change platform, but that can be tricky.
Alternatives are great if only people were using them.
I have a hard time understanding why people are so hard headed on not leaving
The network effect is one reason, if users are responsible for the content then there will be a shortage of content until enough users join.
Beyond that, humans are social creatures and want to fit in. If your community mainly hangs out on one platform, people will want to be a part of that platform. What helps is if people with a large enough following or entire communities make the decision to change platform, but that can be tricky.