Well, remember that all it takes is a few low orbit rockets and about 2 tons of junk with an explosive and you can have a mini-Kessler syndrome, if you do it right...
I’m surprised some govt’s havent though of the idea of shutting off space access this way.
I'm sure it's been thought of many times. The problem is that it takes orbital capability to place the debris in orbit. And once you've got orbital capability, there's a natural tendency to want to use it for putting things in orbit -- which precludes making orbit uninhabitable for your own satellites.
However, should the SHTF for some country with lower-tier space capability, they may well do exactly as you suggest.