I don't think it is easier for Disney to reverse course than it is for the airlines. If they return the air travel mandate there are going to be literal riots in airports and on some flights.
The airlines dropped the requirement instantly, during flights in some cases. There's no reason Disney can't just make a policy change effective at noon. Or they could just instruct the CMs to stop enforcing it.
Air Marshals are there to prevent hijackings and other terrorist incidents. They would not reveal themselves to enforce a mask rule. If they did, a terrorist group could expose the air marshal by having someone refuse to wear a mask before their planned attack.
Airports also have a police presence to enforce the mandate. Disney buses don't. There would not be "literal riots" in airports. It hasn't happened yet, has it? Most travelers comply with the rule whether they like it or not.
As for the Air Marshall, I'm talking about the passengers who get violent, not just the anti-maskers pouting as they try to claim they're taking one continuous sip of their water for the duration of their flight.
Disney also has to consider last-minute cancelations when ending or reinstating a mandate for their buses. Flight tickets are usually nonrefundable because the refundable option is more money - and if the rule changes during your trip you still have to get home, so the choices become either fly and comply with the mask rule or try to rent a car and drive home (assuming the trip is drivable) at the cost of extra time and money. Then there's the PR hit if Disney has to reinstate the mandate and customers cause a stink. People are accustomed to airlines treating us like dirt, but Disney still has a reputation for great customer service (despite the opinion of many here or on other forums). They've had a lot of bad press lately, so I can understand why they might take a cautious approach here and see where the chips fall before making a decision.