Growth is important to any social media ecosystem because you have to hit a critical mass of users to continue meaningfully existing - particularly, you have to have enough users to convince content creators to leave their current environment, since they’re the most likely to be entrenched where they are.
That said, the distinction is that to a corporate/capitalist social media platform, infinite and exponential growth is the goal. To a FOSS social media platform, growth is simply a by-product of the real goal of meeting a public need.
I think the feeling of exclusivity that comes with being early to any scene is neat, but more users means more diversification of instances and communities, and we’ll get to see the blossoming of hyper-specific, idiosyncratic, often deranged communities that made up the best part of Reddit. So growth isn’t all bad.
https://en.m.wikipedia.org/wiki/TERF