I can equally imagine Mears and Disney lying to each other and the public
Lying is too strong a word. Instead, companies carefully craft public statements in order to put the company in the best light possible.
Disney stated:
For nearly 50 years, Walt Disney World Resort has continued to evolve the guest experience to best suit the changing times. As we plan for the future, we are looking at how needs and preferences are changing across the travel industry, particularly in the way people want to get places faster, at their convenience.
Vacationers have more options to choose from than ever for transportation, including ride-share services that save time and offer more flexibility to go where they want, when they want. In light of this shift, when Disney Resort hotel bookings open for stays in 2022, we will no longer offer Disney’s Magical Express service for airport transportation, starting with arrivals Jan. 1, 2022. We will continue to operate the service for new and existing reservations made at Disney Resort hotels for arrivals throughout 2021. Additionally, complimentary transportation options – such as buses, monorails and Disney Skyliner – will continue to be available within Walt Disney World Resort for Disney Resort hotel guests, including to and from all four theme parks.
Disney's statement is intentionally obtuse. Despite "more options", DME remains an immensely popular service among WDW vacationers. Disney is not abandoning DME because "Vacationers have more options." Rather, a financial calculation was the determining factor in this decision. Putting it more bluntly, if DME cost Disney nothing, Disney would still be offering it.
Similarly, if we look at the statement from Mears:
Walt Disney made us aware of their decision. While we are disappointed Disney will no longer offer this service, we intend to continue offering transportation services between the airport and all area theme parks and hotels to meet the demand of our visitors now and in the future.
This does not preclude Disney and Mears from having attempted to explore modified terms, only that Disney made Mears "aware of their decision", whatever that decision may have been.