Why can’t “test prep” then just be fully simulated (as in you come in, same time limits, same setting, etc) practice tests? Or is it more that when you take a

Why can’t “test prep” then just be fully simulated (as in you come in, same time limits, same setting, etc) practice tests? Or is it more that when you take a test, your results will naturally fall in x +- y, so the more you take it the higher the chance for a score in the high range?