Look at it this way.

I know of a small regional community that I have occasional involvement in and maintain an interest in their socials.

A person who started an Escape Room in that community recently posted about how much money he has lost supporting that business.

I explained to him that Escape Rooms are a niche but intense interest and that you need a large population size to support them.

He was appealing to the wider community, of 9000 people, to come in and support his business, but realistically, there's maybe 40-50 people in that community who will actually engage with an escape room. Probably less, the community skews very old.

A "Community" is not a monolith. The only thing you can guarantee the community has in common is whatever forged them together. For a physical community its geography. For an online community its whatever brought them together.

Unless "Craig Mod" built his community around a specific set of shared reading interests, theres no way in hell that its a good general book recommendation engine for the participants.

Goodreads/Kindle/Amazon have shot their categories to hell and are barely more effective than a keyword author search, but for all its failings thats still going to have better book discovery than a random blob of people on a random twitter clone.