You can create more houses on the same land with technology called "taller buildings", mass timber construction, single stair apartment reforms, upzoning, &c.

The above comment saying corporate investors lobby for reducing supply isn't true though. It's individual old NIMBYs and small time developers who lobby for that. Big companies like BlackRock are passively investing because it's so easy when the local government already wants to help them by restricting supply, but they don't individually show up to city council meetings and lobby for this stuff.

You really can defeat them by showing up. No California YIMBY policy has lost someone an election yet.

You're quite right! If only so much of the viable, desirable land wasn't already occupied.

Many of the people currently occupying it would be happy to sell it to you so you could do infill development and they could move to Hawaii! It's just illegal to do it now.

(Or they could stay in place - California requires this to be possible through "right of return" laws.)