Guns and gun ownership are a deeply ingrained and arguably sacred part of culture for a lot of America. A law to outright ban firearms would not be enforceable. Not now, and probably not even in 100 years from now. Not without a secession or civil war, anyway. Too many people would be very vehemently opposed to it and would genuinely rather be shot and killed by law enforcement than allow their guns to be confiscated. Not even a semi-automatic ban or something like that could ever happen; at least not for many generations.

Not everyone feels this way, but more than enough people do to make a universal ban completely infeasible. The question right now is if there can even be any federal legislation passed to address issues like gun access to the mentally unstable and people on watchlists, let alone high-capacity magazines or gun modifications or a ban on certain classes of firearms.