The science as to vaccines and masks was never "settled". it was always going to depend on deaths and the number of people getting sick. It has always been assumed that as they got the virus under control and as immunizations rose the need for masks would diminish. Particularly once they could determine if vaccinated people could infect others and if so. How much.
Only irrational clowns were insisting it was about the government simply trying to control people.
There is no one reason but a lot of reasons . For one the "science" shows that the nations excess deaths are down to pre pandemic levels nationally though some states remain as a slightly higher than average level . The evidence also shows the vaccines work in if not preventing the disease outright by reducing the severity do a manageable level among the vaccinated. Some studies such as one out of Israel (which has vaccinated more people per capita than any other nation) are showing the effectiveness of the vaccines to be as high as 97%, Which means that if vaccinated, the risk of vaccinated people giving it to each other is nearly nil.
Also the vaccines are showing to be effective against most of the new variants such as the the new B1617 variant
With almost 60% of the population having received at least one shot and a lot of people having had the virus. The risk of transmission is getting lower. And the number of people at risk of getting sick severely or otherwise is getting lower. Which means its more manageable. They have also gotten much much better at treating even severe cases.