What possible reasonable benefit would there be to datacenters in space? Why would that even be a concept at all?

Genuinely: regulation. Every other benefit is conceptual at best. If SpaceX controls the entire heavy launch market _and_ they control data-centers in space, then absolutely no one on earth is in a position to control or regulate such a data-center except SpaceX themselves.

I'm not arguing that it's a good idea, but that is the idea.

It's a convenient way to merge AI and spacetech, two hot topics to the retared investor class that rules our world. The reality and feasibility of it doesn't matter.