That sounds great, but how do you enforce it? If 50% are vaccinated and 50% unvaccinated, how do you keep the unvaccinated wearing masks? Especially when they are likely the ones spitting on cast members and raising a ruckus in supermarkets.
The answer: there is no easy way to enforce it. Vaccine passports would be the closest you could get. Ultimately, if you said the vaccinated no longer have to wear masks in public, nobody will wear masks - it's an all or nothing scenario. There's not enough manpower to enforce a divided approach like that.
I know a few of you feel that masks are one of the big sticking points for getting vaccinated, but I've yet to see that in my life. My huge extended family is full of people who refuse to get vaccinated. They already don't wear masks (even they are supposed to) and their reasons for staying unvaccinated are either that COVID is not a threat or they believe conspiracy theories about the vaccines being dangerous and an attempt at government control.
Don't get me wrong, if you could enforce vaccine=no masks, it would be an appealing idea.