Epic bought artstation, bandcamp, and, sketchfab. I don't know for sure, but I don't think any of those are very profitable. They're almost like resume hosting websites for game developers. 3d artists show off their work on sketchfab, artists show off on artstation, musicians show off their work on bandcamp.

My impression is that epic bought them for sort of the same reason Microsoft bought linkedin. They don't make tons of money, but they enhance the pipeline of artists and musicians available to the game industry.

Of course I have no idea if that's why they did it, but epic has definitely shown interest in steering the direction of the game industry in the past, and aligning the talent pool with their way of thinking is maybe a good way to do that.