HR is just the messenger. This rests squarely on the shoulders of Uber's management. They were informed and refused to act. The buck stops with them.
Also, having the number of woman engineers drop from 25% to less than 3% on that team should have been a red flag well in advance of this ever being published.
There's indeed a lot to hang on upper management, but HR has responsibilities delegated to them for a reason. I'm sure heads will roll, but presumably they've been cruising without an HR reboot for years, so a lot of habits and perspectives are going to be entrenched.
I would guess more the former. Execs think it's boring (or worse: a blind spot), consequently don't hire well for the positions, the pretty soon the left hand doesn't know what the right hand is doing.
Also, having the number of woman engineers drop from 25% to less than 3% on that team should have been a red flag well in advance of this ever being published.