It's because of laws against charging the market price, which unsurprisingly has led to perverse outcomes. From the article: Landlord groups don’t dispute that

It's because of laws against charging the market price, which unsurprisingly has led to perverse outcomes. From the article: Landlord groups don’t dispute that thousands of rent-regulated apartments are vacant, and blame 2019 changes to state rent laws that severely limit how much they can charge new tenants for after longtime renters move out.