A lot of people do use Bookwyrm! It just depends on finding the right community.

I am on a fairly small brazilian instance (velhaestante.com.br) and even though I joined while not knowing anybody I still get a fair amount of interactivity. Not enough to be logging in every day, of course, our instance is not nearly as big as something like bookwyrm.social and I don't read and update that often.

It's just like any other fediverse software. Even on a small instance you can get a fair level of interactivity and on top of that you can still interact with big instances and large amounts of content! Of course, if you just create an account and forget about it, or you don't use it very often, and don't seek out interactions/following other people, of course you won't get the same level of content in your feed as if you were on GoodReads.

That's the charm of the fediverse!