I can’t speak for Discourse’s rationale, but over where I moderate and help extensively on all things Discourse, we’ve recently switched from Categories as Homepage to Latest and our engagement has seen very promising rises. We are getting more views, more replies, more topics, et al.
We originally went with Categories as latest to make it feel more like vBulletin, but in the end, it didn’t serve any benefits for our community. Latest gives you a quick synopsis of what is being discussed. That seems to be of value to our visitors and our users.
Sure we had a few people complain but I think all of that has died down now that everyone gave it a good honest try.