The price is also set by developers. There's no reason for rent to increase 30-50% in a single year other than literal greed. Will people pay it? Yes, because they have no choice in the matter, they need a place to live. But it's still greed raising the price.
To be pedantic, the price is set by the leasing office, which may or may not be run by the developer. People do have a choice in the matter: they choose to live elsewhere. If an apartment raised rents 30-50% for no reason, that's what everyone would do and they would get no tenants.
Except, they're not raising rent for no reason. They're raising rent because housing is becoming a scare commodity, and there's way more people looking for housing than there are housing units available. If they look elsewhere the prices would also be high.
The "greedy" developers are the ones that are capable of bringing us out of this situation by profiting off this shortage by building more housing. Hostility to developers is a big reason why San Francisco and similar ares have such high housing costs.
The people actually building the buildings (developers) are, generally, different than the people renting out buildings (landlords). Developers profit when more units are built, landlords are hurt with increased competition.
Also, recent California law was changed so that the maximum allowable annual rent increase is ~10% (still rough if you are hit with that, but better than 30%).
