We all know the pictures of the astronauts on the ISS floating around. We also suspect that a lack of gravity is bad for the body as the muscles go weak and such.
Why don’t spaceships just rotate to cause the effect of artificial gravity through centrifugal forces?
We can’t launch anything very big, and things that are constantly spinning are hard to engineer for 100% reliability especially if you have to assemble them in orbit.
And since we can’t launch anything very big anyway, it would make sense to maximize interior space. Leaving two sides of the craft basically unusable as a floor and ceiling reduces available surfaces in a space by 1/3.