Theres that easy trap to fall into with that question. Why is a kidney shaped like a kidney? Because it is. Is there another shape which a kidney could take? Most likely, but it's shaped like a kidney.
Gotta be careful with why, there are a lot of dead alleys inherent in the question. But yes, we are philosophically concerned with why. Over concerned at times, which leads to the anthromorphization of process and physical forces.
Not in the case of gravity, but it everytime someone talks about evolution choosing a trait for survival I die a little bit inside. It's not a shorthand way to express the idea, it's a wrong way to express the observation. And they do it a LOT. On wide distribution science programs.