Why are impact craters radially symmetric? Okay, so I believe that most of the impact/collisions happen at oblique angles to the planet's radial direction. (I am not very sure about this, but since it is not a freefall, we can assume that the collision is oblique).

So why are most of the craters radially symmetric? 

Why isn't the depression skewed?

I have almost never come across a photograph of a skewed crater.
The main reason why impact craters are close to symmetrically round is because it's the explosion of the impactor, not its collision, that creates the impact crater. The impactor is travelling so fast that, rather than simply exploding on impact, it burrows deep into the collision site, heats up from compression and friction, and explodes deep underground, thus creating a more-or-less perfectly round crater.