I guess it depends on how it is supported. Running a host of this kind will typically cost €200-€1000+ per year depending on popularity.
Is the admin accepting donations and are users contributing? Is it sponsored by a commercial or non-commercial entity? Is the admin a billionaire who likes to tinker with stuff (not that uncommon)?
TL;DR even if it's not a business it needs a business model to be sustainable.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!