The problem is that it only takes one idiot to cause a problem... And the odds of at least one manager being an idiot approach 100%, as your company grows.
(In a place like Uber, though, the problem seems systemic.)
SV encourages people to move fast, be aggressive, don't be afraid to break things, ignore regulations, disrupt all the things, etc. There are substantial similarities to the way a VC-funded startup operates and the way a pick-up artist operates.
You'll notice that Susan Fowler's blog post also goes into detail about the Game of Thrones-esque culture with middle managers constantly and openly plotting to overthrow their superiors and take their jobs. A culture that encourages you to figuratively fuck your boss also encourages you to literally fuck your subordinates. It's a culture of aggression and proving your dominance.
Big traditional conservative companies on the other hand... well, they just don't have that culture. Their culture discourages people from taking risks at every level. In order to get anything done, you have to go through several layers of bureaucracy, put everything in writing, make sure your is are dotted and your ts crossed. It discourages aggressive, disruptive risk-takers from coming near the company. And without aggressive, disruptive risk-takers, you don't have nearly the amount of sexual harassment. Yes, it still happens on occasion, but it isn't nearly as systemic or as blatant as in a VC-funded startup.
So it leads to the seemingly-paradoxical situation where the best companies for women and LGBT people to work at are the kind of "conservative" companies that you can imagine Ned Flanders working at. But culturally conservative isn't the same thing as politically conservative; I've said this before, but I have a lot of politically liberal friends (most of them enthusiastic Clinton voters) who live in the suburbs, work 9-5 at traditional large corporations, and have traditional families.