I'm not sure it is that cut and dried. They put a lot of development into the free system too, and I don't think "no one has an issue" with it - it is confusing and frustrating to first-timers, requires a lot of extra criss-crossing of the parks, and discourages park-hopping because of the need to be in the park in the AM to get a FP that potentially has a PM return time. And an expansion of the system comes with its own benefits for Disney, in more consistent, predictable guest traffic patterns and in further freeing of guests to shop/snack/indulge in extras rather than wait in lines.
I'm sure Disney is also aware that one of the few areas where guests speak more highly of Universal than of Disney is on FOTL vs FP, and while they can't mimic that system exactly because of the differences in scale they do likely see the benefit in improving their offering.