I would rather my DAW company concentrate on new features and better workflow than give me some new loop library, instrument or plugin.
Yes Apple (logic) owns a large Apple loops library and yes the stock plugins are ok but there are much much better sample libraries, instruments and 3rd party plugins available than what your stock DAW will give you.
Many Logic users get stuck with the stock sounds because they are, like you said, easy to get an ok mix from.
This is not the way most pro’s work. If you don’t like the stock stuff find better 3rd party alternatives, You’ll blow your stock logic buddy’s session out the water.