The bus setup means those with disabilities along with the nature of having a disability means it naturally takes longer to get from point a to point b, even within the parks to a degree, but especially when park hopping due to having to wait for multiple buses (especially for those that also have mobility devices), but contrary to popular belief not everything has to be done to ensure the wait times are equal, if it did, the
DAS system would be far different than it is as it often results in longer waits. Yes, there are trade offs, but if you think the waits (count all time spent waiting after getting a return time and after returning) are the same or shorter than other guests, you are lying to yourself.
And just for the record at
Disneyland the official reason you are allowed to get a return time for the other park is for the very reason I mentioned, it takes longer for those with disabilities to travel from point a to point b. This is even more true at WDW, which is why I say it should be allowed there as well, as the same logic applies, just to a greater extent.