Not offered on BNE-SFO a few weeks ago. I think they were available as I saw a few people wearing them, but very few.

On the return SFO-BNE, they were proactively offered, and I think I saw more people wearing them than I've ever seen - easily 50% of the passengers in the front business class cabin were wearing them!

(Both flights had slippers at the seat, as they always do on this route)