Problem is the actual size of our military. Some 475,000 in the Army of which the bulk are support people, not front line soldiers. Some 100,000 Marines , and while the attitude is ‘every Marine is a shooter’ the reality is there are still a significant portion that is support. Not near enough people in the active military to put down a revolt. So you would have to call up the reserves, and that becomes highly problematic. Who would they fight fo4, the government that has become insulated from mainstream America, or would they form up units and fight against the government and it’s supporters.
You point to things about our military that can be exploited in an internal conflict. It’s big, bureaucratic, expensive to put soldiers in the field. It would be more vulnerable inside it’s own country than a foreign one because it depends on the infrastructure of its homeland. Who will pay for and man this behemoth with their country so divided, and factions willing to disrupt commerce and its own infrastructure? Our military is very effective in foreign wars. This is different than a foreign war.
You get it, most don't. It's just math.