I tend to agree that the attitude is sour grapes on the part of the other companies. When I travel alone, I tend to use the shuttle service, when I go with my family, we usually rent a car and go other places.
I frequently go to Chicago, and when I go there, I stay at hotels that offer a free shuttle to and from the airport. When you go to O'Hare, there is a bank of telephones people use to call the hotels when they arrive to get the free shuttle. Lots of hotels use them. However, they are the hotels at Rosemont, and not downtown Michigan Avenue. That is fine--my meeting is at Rosemont. I don't see the Chicago taxi drivers complaining about the free shuttles.
The two times I went alone with my son to WDW, we took the Mears shuttle. It was nice, because then I didn't need to drive in an unfamiliar area, and it was much cheaper than renting a car. If we went without Dad again, I would use the shuttle again. If ME were available, free, I would use ME. Otherwise, I would choose whatever means of transportation was least expensive while still fulfilling my needs.
The problem, as I see it, is that WDW is a bigger draw to Orlando than Rosemont is to Chicago. The other transportation companies were tapping into the WDW business. But, business is competitive, and consumers have only a limited amount of money to pay for a particular service. A smart consumer pays the least amount of money for a particular good or service that adequately meets their needs. I don't mind being on a bus with other people going the same way I am. It doesn't take a significantly different amount of time to get to WDW from the airport, whether I take Mears or when we rent a car. When I take our usual ATA non-stop from Indianapolis, we get there about 11am, and we are usually at the park, reliably, no matter which method we use by 3pm.