I agree it's a problem Peter. I'll offer a couple of opinions.
(1) Too many instructors have never done any real A-B flying. They have probably spent years flying around the same small patch, and given how very badly they are paid, they certainly don't have the spare cash to go off on the sort of long trip you and I regularly enjoy.
(2) Flying schools are not teaching people to fly. They are teaching people to pass the test. The difference is marked and important - if they know that examiner X prefers route Y, then the school will simply not spend a students money how to fly to Z.
Not satisfactory, and probably best solved by moving away from the school model to a truer club environment where people help each other out and students or instructors actually use aeroplanes as god intended - do to fun stuff over long distances, rather than short fixed routes flyable within an hour and coming back to your start point.
G