The problem here is, if all the people they let in are vaccinated, then they don't let in anyone who is not vaccinated. Vaccine passports are great, except you have now cut off the business opportunity of selling tickets/hotels/over priced mouse shaped ice cream bars to people who are not vaccinated, of which there will be many who also have the disposable income to purchase over priced mouse shaped ice cream bars for their 4 children. There are a whole host of people who will not be getting vaccines, and do you think it will help Disney to tell those people they don't want their money? If Disney were to reach capacity with only vaccinated guests, then passports would be a dream scenario for them. However, they were only reaching capacity a few days a year at a few parks pre-covid when everyone could come, vaccinated or otherwise. So, it stands to reason that they will not fill to capacity if they opened and denied access to a sizable portion of their clientele.
Now, Disney may decide it has made enough money over the years, and will be content to run a business that chooses not to accept dirty, unvaccinated money, but I would imagine the shareholder would not take kindly to this. Also, Disney being the entity that it is, I have a hard time envisioning them (or any for-profit business) turning away my money simply because I'm not going to get a vaccine.