John,
The reason is that, although the rules are 100% created by coaches, athletic directors, and commissioners (who are almost 100% former coaches), those same people, as well as virtually every on-field coach, offer NO support to officials who attempt to enforce those rules. In the first few seasons that the NCAA attempted to make enforcement of those rules a “point of emphasis,” virtually every attempt - coast to coast, border to border - to get compliance on game day were met with great resistance, and criticism of officials by coaches and school administrators of officials being overly officious. And, the pants get altered to the point they can’t be brought into compliance, and all we hear from the coaches is, “That’s what the uniform suppliers sent us!” And, if we tell them to get pants with longer legs, they give us, “That’s all we have. We don’t have any more pants.” So, the rules makers started using a term, “Significantly out of compliance” as the standard for unacceptable pants. That changed nothing, and still no support from NCAA leadership. Bottom line: coaches don’t care, and they aren’t gonna risk offending their players to the point they don’t stick around (there is a transfer portal, you know).
You won’t hear NCAA officials state this, publicly, but everybody gave up on enforcing the pants/knee pad rule a couple of years ago.
And that’s that.
You can add mouthpieces to that same phenomenon. And ‘towel tails.’ Oh…have you actually seen any hip pads, lately? How about those undershirts hanging down to their thighs?