I am curious if this is as much a reflection on not knowing how to practice, versus only playing at it. If I weight lift but never progress above a 1kg weight, I would not be shocked that I don't get any of the advanced muscle benefits of weight lifting. Same for pretty much any physical exercise. If I don't push past my current limits, I am not surprised at lack of growth.

To that end, playing sudoku, but only staying at the "1 star" difficulty puzzles, I don't know why I would expect brain growth, as it were. Learning the strategies and modeling that is needed to solve the advanced ones, though, is a very different thing.