Delta shows the same viral load in vaccinated and unvaccinated people, which means it's much easier for vaccinated people to transmit Delta than the original virus. That's the reason for the reversion in masking rules.
Vaccinated people remain at far less risk of hospitalization and death with Delta so that risk remains with the unvaccinated. Personally, I say fuck the unvaccinated and let them take the risk and don't revert to the old masking rules. I also would drop Covid coverage for any unvaccinated people if I ran an insurance company but I'm an asshole.