They didn’t have those at the time, you need infantry to support tanks. I am more afraid of marauding packs of criminals should the grid fall. Even with isolated riots, the government pulls out of areas and lets law abiding citizens/businesses fend for themselves. Imagine if there should be a major conflict (downfall of order) it’s not the government you have to worry about it’s the scum who depends on the government who will have nothing and stop at nothing to obtain sustenance.