SF has a complicated review process that basically lets neighbors hold up permit approval indefinitely with appeals. Whether good or bad, it's there. Shadow laws are also in place and would need to be changed.

Changing a low to mid density neighborhood into a high density 12 story building neighborhood means a lot more than just removing height limits. Sufficient parks and retail/commercial space need to exist to ensure good quality of life, no one wants to live in a neighborhood full of condos & apartments and little else.

Likewise, there needs to be sufficient transit, SF Muni is already bursting at the seams, add a high density neighborhood without adding transit, and no one will be able to get out of the neighborhood.

Building high density housing is important but it's a lot harder than just removing a height limit.