Why do hairdressers cut off too much hair even when you tell them "that's enough?"?

When will I ever learn? Most of the time when I go to a beauty salon for a trim , or especially a style, they cut off massive amounts of my hair! When I say, “ok! that’s plenty” they keep cutting. Q: why do they do this? Is there some monetary reason? She had a razor and comb and just kept chopping away. Now it’s so short that, which hasn’t happened before, it is growing back very unevenly and I can’t make it look presentable. All the other times, hot rollers were able to fix it as it grew out. Is there a reason this happens? At least the bangs are long, thank heavens.