The NMD program is limited in scope and designed to counter a relatively small ICBM attack from a less sophisticated adversary.
also ground-based interceptor is more expensive than ICBM, and you need one for each warhead and maybe also for decoys, and probably more than one to be reasonably sure. since everyone operates under MAD it doesn’t matter if you destroy most probable adversary’s nukes on the ground or in the air, so that’s one of reasons why ICBMs are a thing, and then SLBMs as a second line. cue arms race. ABM are considered destabilizing and are limited by treaties
you would need something silly like 50x more interceptors than ICBMs and SLBMs and these are more expensive and technically harder than either