On Android most well-architected applications will persist almost everything to disk before showing it to the user. Network directly to UI is too unstable.

It's not about intensive reads/writes (dozens of MB) it's about making each individual read or write very fast so you don't drop frames. On Android you have 16ms to draw each frame (60fps). If you have a DB request take 5ms then all of a sudden you're very likely to have jank in your app.