Because of the Delta Variant, which seems to have originated in China. It is much more contagious than the original, and while it seems that the current vaccines are effective against it, full data isn't in yet. It's starting to spread significantly in the UK and elsewhere...

People think it's all over and past; it isnt. People are still getting sick, hospitalized, and dying. The curve is going down in the US, but it's started up in other places.