Developers aren't a cartel, but they respond to incentives just like anyone else.

https://www.fresheconomicthinking.com/p/upzoning-predictions...

For one example of how upzoning alone doesn't result in developers exceeding the market saturation rate.

To be clear, I support upzoning but I think it should be accompanied with an increase in the holding cost of land, so landowners are incentivised to develop now rather than later.