> At some point these community efforts must grow back into a company again, right?

(a) Not necessarily, it might turn into a non-profit organisation, a cooperative, or something “akin”.

(b) Nothing wrong with companies either. Although I (and many others) would prefer option (a), a fairer company that respects its customers’ needs and rights is very welcome!

Except that company doesn't own the infrastructure because it's decentralized. <Insert your favorite article about decentralized systems here.>

Probably around the 1200-5000 mark you might start seeing market segmentation, and then a federation of local mesh networks' super hubs all sharing a dedicated backbone of some sort and cost sharing. Backbone and last mile always seem to get separated out pretty quickly as they're different businesses. Not all nonprofits need to scale to unicorn size.