I think you underestimate the number of us old farts still lingering around. One of the great things about the Fediverse is that it gives us the old Web 1.0 vibes which we appreciate because we remember the early Net when all this was fields and you could buy an ice cream for a penny and still have change to catch the matinee down at the pictures and... Where are my bloody slippers?
...the eternal september started before NCSA mosaic was released; i don't think any website can really capture the feel of the original internet unless it's structured like a text-based terminal...
The problem with attempting to run a serious social media instance is that social media needs new content all the time or nobody will really ever check it... however, there is often not nearly enough good, serious, content to support it long term.
Fun fact: The time since October 30th, 2022 is also referred to as "Eternal November". That's because November, 2022, when tons of completely clueless and often obnoxious newbies came flooding from Twitter onto Mastodon in expectation of an all-out Twitter-before-Musk clone and not knowing anything about the Fediverse, has seemingly never ended.