> How? Two ways: 1. Some people will naturally want to move out of their rent-controlled apartment, for example to be closer to a new job or to get more space

> How? Two ways: 1. Some people will naturally want to move out of their rent-controlled apartment, for example to be closer to a new job or to get more space for a newborn. Those people are disincentivized to move because rent control means they are currently paying below-market rent. Incidentally, that also increases traffic congestion because nobody wants to move across town to be closer to work. So you commute to where I live and I commute to where you live, instead of us both living within walking distance of work. 2. Rent control normally does not include an adjustment for inflation. And, when it does, the rule is usually "rent can increase by x% of rent or y% of CPI, whichever is lower ". That means that over decades, rent falls in real-dollar terms. Since potential landlords can do math (they have that technology) they can see that the ROI of an apartment building (measured in decades) is lower in places with rent control. That disincentivizes them to buying or building apartments. Lastly, it seems like you're really trying to hang your hat on zoned capacity. The thing is that zoning can change. If the ROI looks right, landlords will lobby the city for a zoning variance to increase capacity. If it doesn't, they won't.