Because people are willing to pay it in Disney apparently!
I agree with you, OP, completely! We have only stayed at Hard Rock and Cabana Bay in Universal, but they are far superior to their Disney counterparts!
Hard Rock was far and away better than any of the Disney deluxe resorts we have stayed in, and we have stayed in almost all of them. Plus you have the added bonus of being able to walk to both parks and City Walk! We really love the Poly and WL at Disney, so I am not knocking them, but the quality and amenities at Hard Rock were better for a fraction of the cost! I think the most we have paid at Hard Rock was around $250 a night, military discount, Christmas week. Other stays have been a little lower.
Cabana Bay is basically Universal's value resort. To be completely honest, there is no comparison! It far exceeds each and every Disney value resort, and for the most part Disney's moderate resorts as well. The pools at Cabana Bay are even better than some of the Disney deluxe resorts. We have stayed in a family suite, 6 people, over 4th of July week for just under $150 per night with military discount! I am paying $152 per night at a Disney value with military discount in late May, in a room that only sleeps 4. At CB we were walking distance to the new water park, and never waited more than 5 minutes for a bus to the parks.
Universal's resorts win in every category! Disney simply charges what they do because people continue to pay!