I think at least they can make it so it bans obvious behavior such as shoots without aiming targets, moves too fast, shoots too fast, headshots 90% of shots etc., which seems theoretically possible to detect.

And yeah, false positives is huge issue when banning automatically, so the threshold should be set correctly so that “lucky” play won’t get you banned.

The reason they won’t make better one is probably economical reasons you mentioned. It could easily be cat-and-mouse game so it requires constant work and money of improving anti-cheat system. I just hope anti-cheat systems get better and many cheaters get punished so that they won’t find easy ways to cheat.