There's the possibility that the USG believes the dollar's primacy is going to come to an end in the relatively near future. There are other factors at play that could weaken the dollar's status that matter more than sanctions, including:

(1) The geopolitical shift away from a unipolar world, with the rise of states such as China.

(2) The upcoming end of the petrodollar, as nations shift to renewable energy.

If you believe the reign of the dollar will come to an end anyways, you might as well use its power while you have it and throw sanctions around to weaken your rivals.