Why do people never learn how to cut their lawns properly with Tall Fescue or Bluegrass?

Tall Fescue should not be cut any shorter than 3" and same with blue grass. In fact, 3 1/2 to 4" is even better. I cut my at 3 1/2" and it needs less water , and rarely has a weed and doesn't burn in the hot summer months....People spend thousands of dollars on new sod and sprinklers and don't learn basic Mowing 101? I don't get it?