Mastodon instances have certainly gained tons of new users...but, wait 'til some people learn that the fediverse has been around since ~2008, and the current numbers are far higher than *only "mastodon"*. For example, i'm seeing over 6 million accounts as captured before end of October: https://fediverse.party/en/fediverse/

Of course, on the fediverse, no one cares about adoption numbers. :-)