Because challenging someone to "justify" why they feel sexually harassed is inappropriate?
And that leads to a country where every manager is absolutely terrified to be accused because they know they'll be automatically guilty.
In the OP case, the manager clearly behaved completely foolishly, but i have actually met people in some offices that were into open relationships, and talked extremely freely about sex, just like any other subject ( though he did have some weird behaviors, but it didn't prevent people at the office from working with him). I wonder if that Uber guy wasn't like that.
1. He was propositioning her; not just "initiating a topic".
2. That person was her manager, which changes the picture altogether (see this comment by 'calcsam: https://news.ycombinator.com/item?id=13682117)