A 'perfectly' micro-ing AI is both boring to implement and boring to play against. Somebody made one for SC2 back when that was popular, take a look at these videos to see how uninteresting it would become after the first attempt.
yeah but I'm pretty sure these bots still get crushed by humans because of macro, planning and positioning, which is why it takes top firms on the planet so long to solve the problem
If the AI wasn't very smart, then you'd expect there to be some optimal path that would beat them. But Starcraft has always been a game with very little skill ceiling on micro. Well micro'd units have the potential overcome huge macro advantages. A famous real-world example would be Boxer's Immortal Marines: