It would make life simpler if it did count but it would go against the history of our game. When the basket was designed, it was a representation of the original target which was a tree with two bands of tape wrapped around it. If your disc hit the tape or between the tape, you had holed out. There's no way to hole out on a tree or pole from above the top tape, so Steady Ed did not want landing on top of the new basket to count.
You say, "Well, why does sticking below the basket rim count?" The rationale is that disc can enter the basket coming over the top of the basket rim and try to exit out the side and wedge in the basket. On a tree, that would be like a loft putt where the disc is moving downward when it hits the tree properly above the tape. If the disc, could have traveled "thru the tree," it might have stuck on the way out the other side like in a basket. So you say, "But if everyone sees the disc wedge in the side of the basket from the outside, it was never high enough to be in." That's true. However, one of the benefits of the basket invention was that you could finally tell whether a player holed out on blind holes because the disc was in the basket. Since a disc on a blind shot could wedge in the side of the basket from the outside in or the inside out, the rules give the benefit of the doubt to the player. So, for simplicity, wedgies have always been ruled as good based on the "benefit of the doubt" rule given to players EVEN if it was obvious the disc wedged from the outside.
So, even though it seems logical for first timers to believe landing on the basket should also be good, the question is whether we throw out this historical tradition from the origination of the sport for that convenience of simply having any disc suspended by the basket count as good?