'As good as it gets' means 'the thing's not going to get any better because it's the best' right? But my non-native grammar sense strongly gives a question that why you don't say like
It's as good as it could get.
It's as good as it has gotten.
Searched some other posts about it, and there's this guy said that the phrase, 'it gets', means 'it has reached at some point' or something. Then, why do you still use present tense?