Also because many of us who are getting vaccinated aren't fully protected yet. Keep in mind that they just opened it up to people 16-40 less than a month ago in many places, and it takes at least
I'm in California. They just opened it to 16+ on April 15, and appointments were very hard to come by the first couple weeks as people were first eligible. It takes 6 weeks from first shot to full protection, so even assuming someone got an appointment the very first day, they wouldn't be protected until the end of this month. The effectiveness rate after the first shot isn't fantastic - it's much better than nothing, but nowhere near the level of protected I would want if I were at Disney and suddenly no one was wearing masks anymore.
Throughout this pandemic, people have made decisions based on whatever metrics or risk assessments they value. I know we did when we went last winter - considering what we felt comfortable with, what made us uneasy, even choosing airlines based on how full they were packing passengers and how good their mask enforcement was in general. There were things we chose not to do that others did, and that's perfectly fine. But this is a huge change with no warning whatsoever. Prior to this week, Disney had 6' distancing, mandatory masks everywhere except while actively eating and drinking, and a lower park capacity. Suddenly without any warning whatsoever, all of those protections are out the window. If I were at the parks this week, I would be really ticked off, because I would have been promised protocols to help reduce spread of the deadly virus, only to find that those protocols were no longer in existence without a change in the medical realities of the country. Only 1 in 3 adults is fully vaccinated, and no one under 16 is. While kids have a lower risk of severe covid cases, we know they can be carriers and transmit cases to adults who do get severe cases. Given how much of a struggle it was to enforce people wearing masks before, I can only imagine how much worse it will be if people only need to wear them intermittently. I can't imagine people will have the masks on in outdoor lines, even when packed together now, waiting for long periods of time because park capacity is back up to "normal busy day." So in essence, there are no longer precautions being taken at Disney - and people have a right to know that when making their decisions about trips.
No, no one is preventing me from wearing a mask. But as experts have pointing out consistently over the past year, the mask isn't to protect yourself - it's to protect others. It protects the wearer a little bit but certainly not completely. So if you have asymptomatic covid, and I'm wearing a mask but you're not, the chance that I will contract it is significantly higher than it would be if you were wearing a mask.