It's not that people aren't sticking around Mastodon.
There's more active users now than there were in September. Back then, there were only ~50,000 active users per month on mastodon.social.
It's that a certain segment of registrations were done either in protest, or as a Plan "B" if the Plan "A" (Twitter continues to be a going concern) fails.
That said, if Mastodon is seen merely as a Twitter alternative it will fail.
