That's simply because memorization is about the only technique that can be taught reliably across a wide range of learning styles. Anything that involves deep though has to be individually tailored to each student.
Case in point -- one of my step kids did real well in math in grade school, until the teacher started mixing in art to make it more fun (one project was to make a "math cube", and decorated it -- he failed that project). The other kid was out the week that fractions were taught. She heard from her friends how hard it was, and was terrified of going back to school. So her mom taught it to her (known her learning style), and she aced the test when she got back. All other students in the class failed miserably. (And the teacher was extremely upset -- how dare a parent actually teach their kid -- that's the teachers job).
Case in point -- one of my step kids did real well in math in grade school, until the teacher started mixing in art to make it more fun (one project was to make a "math cube", and decorated it -- he failed that project). The other kid was out the week that fractions were taught. She heard from her friends how hard it was, and was terrified of going back to school. So her mom taught it to her (known her learning style), and she aced the test when she got back. All other students in the class failed miserably. (And the teacher was extremely upset -- how dare a parent actually teach their kid -- that's the teachers job).