It's the same with a lot (probably all) of sports. I've played tennis semi-seriously since I was four-years-old (by late-teens I could hold my own with people who got tennis scholarships to the states (I'm in the UK)), and by far the best way to get better is to play with people who are better than you.

If you just play with people the same level, or if you are the best amongst the people you play with, you have no reason to learn new techniques or figure out how to read serves or position yourself on the court etc.

For example, when I started playing with the scholarship guys I had to learn a kick second serve (top spin serve that bounces very high to opponent's backhand) or they were just smacking them for winners every time.

Obviously you can't advance too quickly or it would be like neophytes playing with experts, but amongst the people I played with it was accepted that you always wanted to be playing the people who were better than you.