

Because it’s expensive.
You have to build equipment to withstand constant load, which is much heavier, which means more launches and launches are more expensive.
Suddenly there is a greatly reduced working and living area. You go from being able to work in any surface to only surfaces near the “floor”. So you need to build more areas, and the architecture becomes more complex, both requiring many more launches.
A lot of the things you want to do in space, like science experiments, have to do with micro gravity, so introducing artificial gravity would make space stations kind of pointless.
To make the structure big enough to spin comfortably would require a very large structure, which means a lot of material, and a lot of launches. And more places for things to go wrong, so a lot more engineering and safety assurance is required.
Yes, but thats a small area compared to the entire station.