I would imagine it’s expensive and time consuming too? Maybe they are doing it, but seems improbable that thye are sending out samples from all over the US to be tested in special labs?
Just a tiny state like NM has done 4 million tests since April 2020. Thats about an average of 250k a month. Very doubtful they send many of those swabs in for the type of testing needed to declare variant takeover in the magnitude of this delta declaration and now the new lambda et al.