It’s easy to imagine where the money goes out, but where does the money come in?
Obviously the answer is “the users” but that’s the problem: Not many users are going to be interested in paying ongoing fees just to exist on a social network when they can get the same thing for free.
There will always be a core group of true believers who will pay for these networks, but the networks aren’t very useful if it’s limited to a small group of people willing to go through all of the trouble and keep paying just to exist on it.
This is the big question that a lot of the web3 conversations conveniently sidestep: How much is it going to cost? Everyone seems to assume some hypothetical future blockchain that costs very little, but the bottom line is that you still have to incentivize all of the nodes and peers to keep the data and you need to do so in a decentralized manner that will always be orders of magnitude less efficient than hosting on a standard cloud server. That inefficiency is expensive.