Steam Deck made people realise how useful the trackpads are for controlling games, especially FPS or mouse-driven titles. Plus the Deck having a dock means you want a decent controller for it. Combine those two together and you get people wanting them to use when docked, since trackpads are super useful in some cases.

There’s a whole load of mouse-only games I’ve played docked to my TV using the Steam Controller, and it has kind of Just Worked.