Can't we shoot down most missiles these days relatively easily? I mean, we did obliterate a satellite.
Uhhh, no. Probably one of the hardest things to do actually, especially considering how many different types of missile are out there. And MDA as a whole does not have the best of track records at it. The Navy component of it is where they have made the most 'money'.
Satellites have known orbits, even ones that are falling out of the sky. It is kind of like blowing up the 9:30 train, pretty easy to do compared to a missile. You may or may not know when and where a missile is going to get launched at you, expecially if the launcher is mobile. Kind of like a dirt bike coming at you from the woods somewhere in front of you, or maybe behind.
A very hard target, and a very hard problem to solve.