not enough of those famous and important people moved from Twitter to Mastodon
This is the reason I'm still using Twitter. I use Twitter not to tweet about what I did, but to get news from people I follow.
Tech people can move to Mastodon because their circles are moving, but not with common people.
For me, personally, Mastodon is like empty void. No one to follow and I can't interact with people who share same interests because they only exist on Twitter (since the "famous people" isn't moving from Twitter)