Renting and purchasing are not perfect substitutes. There are many situations where a rental is a far better solution.

This kinda reminds me of student loans, why not get as many people as possible into 6 figure debt?

Yes mortgage is often cheaper than rental, but the whole tradeoff is the commitment, just like all kinds of services, if you pay 40 years up front you can get a good deal, but do you really want to take out a loan to do that?

Limiting landlords ability to buy property is reducing demand for construction, you want to increase demand for housing, not decrease it.

As I said in a sibling thread, it does suck that property owners are incentivized to raise their property values, preventing supply from reacting to demand.

Lowering prices would also disincentivize anyone to sell their house, sort of like the recent, relatively high interest rates. Those undesirable rates have not applied significant downward pressure on prices because they’re simultaneously exerting downward pressure on the volume of houses available for sale. No one wants to sell their low rate house for a higher one.