While they may not be limited, you would have to think that the waiver request has a higher probability of being approved using a noted exception versus trying something completely different. As for the major issue, that isn't as hard to accomplish as you are making it out to be. 60% is just a little over 2 years, call it 2-1/2 years of scheduled classwork. For most majors, the first almost 2 years will be general core classes, which will work almost no matter what major you pick, and is why changing majors in the first 2 years isn't that big of a deal. Now certainly there are majors for which that isn't true, but for most it is. Then you also have the replacement classes, or in other words, classes that aren't exact to the class required for the major, but is an acceptable substitute, of which the school certifies that, which means UK has control there, and outside of trying to substitute a class that really has no connection to a required class, they can make stuff fit. And if Sarr did in fact attend summer school at UK, he could have made up ground on the major that was chosen, allowing him to meet the 60% rule by the fall semester.
Even beyond all that, we aren't talking about the common guidance counselor helping him choose a major that fits the requirements, UK has people for which these kinds of issues are their specialty. If they chose a waiver for a reason not noted in the exceptions, then they would be totally at the mercy of whoever is making the decision, whether it is a good argument or not. At least by choosing one of the noted exceptions you have something stated in the rules that help your case. While I'm sure you can request a waiver for something not listed, the rule reads as though the 2 exceptions are the only waivers they will consider. As the rule reads, the institution can request a waiver for.....and then lists the 2 exceptions, which indicates that even the noted exceptions aren't required to get approved, just says those are the 2 for which you can submit a waiver.
And while the SEC would be able to keep UK from getting the automatic SEC bid to the NCAA tournament, not sure they can keep them from getting an at large bid. Now maybe they have enough pull to make the NCAA not consider UK for a bid, but I'm not sure they can outright deny UK by themselves. Having said that, there is next to zero chance UK would play him if not cleared by the SEC, but it would be more likely that UK would go down the route of trying to force the SEC to clear him, via threatening. And if the fans really got on board, they could really hurt the SEC by choosing not to attend the SEC Tournament which generates a bit of money for the conference internally.