It's the finance industry culture. Why?
Finance is a zero-sum game. That leads to a set of incentives where what you need to do is beat the next guy.
Tech is almost the opposite of a zero-sum games. That leads to a set of incentives where what you need to do is crack a complex problem. Cracking complex problems requires collaboration.
I have been on boards in the valley and in NYC, and I can see this very directly. The NY VCs were far more transactional, and more aggressively willing to drop a company and take the loss early.
Not that it's rainbows and unicorns in the valley! The VCs, after all, work for their customers (err, "LPs"). I've noticed that as the valley VCs are more and more frequently finance rather than former operating guys that they are more like this. I saw it in the dot-com boom, and guess which VCs got shellacked? Mostly the finance guys.
It leads to a lot of savage energy channeling through the system, a lot of deep career dissatisfaction and a feeling that someone, somewhere is tightening the rack, with you on it.
I suspect the only real winners in the city are the landlords.
Whatever the cause, in all my time on the road I have never come across such a congregation of pessimists as I did in New York.