They can, but won't, unless the situation gets so bad that it substantially affects their business. Right now, that isn't happening. I don't agree with all the posters who say people visiting WDW prefer mitigations or won't visit unless they're in place. My belief is that the people who are going now are the ones more inclined to take what they perceive to be a small chance of getting sick. Not saying everyone - I'm sure there are some (probably posting here) - who would prefer to visit with a mask requirement.
But if things get worse, that could change. At that point, it might be worth it for Disney to check vaccination status and hand out the wristbands. Chicago is hosting Lollapalooza soon, and people attending will be required to show a vaccination card or proof of a negative test to enter. If that's the road we have to go down, then we'll have to figure out a way to make it work. At this point, after mitigations were dropped, I just don't see vaccinated people shrugging and going back to mask-wearing without a great deal of pushback. I'm aware of the position of our leaders, but this is a fluid situation that could change with changing circumstances. Hopefully, it won't get that bad.