It makes sense that general purpose instances would have the most users. I'm not a programmer so while I could still register there why would I pick programmer.dev?

The bigger issue I had in picking an instance was just in understanding the differences. I think it would help if instances advertised their stance on defederation, moderation, etc... to help people make a decision (or even to see that lemmy.world may be more similar to some other instances than they might think).