A bunch of things. Planning is hard, real estate is so expensive that people fight anything which might obstruct their view or lower their hard-bought property values (understandably), rental laws are skewed heavily in favor of tenants, and the whole process is hyper-politicized at the neighborhood level. I'm surprised the planning commissioners get anything done sometimes. Public hearings sometimes go on until 2 or 3 in the morning if it's something contentious.

Any large building requires several million and several years before it can even break ground; last year a developer who had already dug a foundation ended up filling it in again and selling the land after a 3-year delay. Also environmental law is used obstructively in a great many cases. I'm generally in favor of public consultation, regulations etc., but sometimes the big projects suck up all the political oxygen and that makes it harder for smaller developers to move forward. The recession hasn't helped either of course.

I'm not in real estate or anything, just a bit bummed that our city government hasn't been running well in recent years.

The reason you will never see any six-story buildings built is the building code. Four stories is the tallest you can legally build with wood framing; higher than that, you effectively need steel framing, and the code requirements for those don't make any economic sense until you get to 10 stories. In between is a dead zone where it is uneconomic to build.

Interesting to know! I'm OK with 10-storey buildings, I think we could build a ton of those in areas like SoMa without injuring the character of the city any.