Server costs, lawyers, management will add up eventually. Ads or other financial incentives will take part in this at some point. The biggest instance, which will have the most funding, could monopolize by defederating others. Though with future account portability it could be made impossible. As in if reddit was the instance, most communities and users would seamlessly move over to others. But right now the risk is real.

Beehaw just defederated lemmy.world and users have to either move with the bigger fediverse of lemmy.world or stay confined to their isolated instance.