The fediverse is not a single database or server. It’s a protocol and standard that’s distributed by design. The fediverse as a whole cannot be centrally monetized, just like email can’t be monetized. A single provider could potentially choose to try to monetize either by requiring a subscription or showing ads, exactly like email providers do, but if you ever feel like they’ve stopped providing a good service you can just switch to another instance just like you can switch to another email provider.
Unlike a centralized service like Reddit, you’re not locked into a monopoly. Switching instances does not lock you out of the system as a whole, just like you can still receive email if you switch to another provider. With Reddit you can only access the platform through Reddit because it’s a closed source centralized monopoly.
One thing the fediverse seems to lack as far as I can tell is a way to link accounts, like how you can set up forwarding with email, which helps you switch providers. But the protocol and standard is still being developed so maybe that’s something that can happen in the future