Generally, it's easier to make things strong in compression than in tension.
In a low-wing plane, the weight of the aircraft is on top of the wing; in a high-wing aircraft, it hangs from it.
It seems to me (I'm not an engineer) that the area of attachment in the latter case has to do a lot more difficult work (suspending the rest of the plane by its bolts) than in the former (bearing the weight from below).
And since in a high-wing aircraft all the structure is in tension (everything is hanging from something above it), presumably it's not just the wing and its attachment points that are affected, but most of the fuselage that has to withstand this tension.
Are these intuitions true, and if so, what are their engineering implications?