Remember the Kosovo War. Even though the US suspected armor on the ground were decoys, that had to hit them anyway just in case. How many decoy silos can China make all over inner Mongolia?
The US does not have tens of thousands of nuclear missiles though.
The US stated in its March 2019 New START declaration that 1,365 warheads are deployed on 656 ICBMs, SLBMs, and strategic bombers. The total stockpile is about 3800 warheads.
It takes 2-3 warheads to guarantee a kill on a silo so by building 500 silos, you'd be wasting a large portion of the current US nuclear stockpile.