Decentralization upends the social network business model by dramatically reducing operating costs. It absolves a single entity of having to shoulder all operating costs alone. No single server needs to grow beyond its comfort zone and financial capacity. As the entry cost is near zero, an operator of a Mastodon server does not need to seek venture capital, which would pressure them to use large-scale monetization schemes. There is a reason why Facebook executives rejected the $1 per year business model of WhatsApp after its acquisition: It is sustainable and fair, but it does not provide the same unpredictable, potentially unbounded return of investment that makes stock prices go up. Like advertising does.
Source: Why does decentralization matter? by Eugen Rochko (December 30, 2018).