Landlords generally aren't going to decline making money. If they're not renting these units out, that implies that doing so would cost them money despite the rent they would receive. You can force them to rent the units out anyway, but ultimately they're not going to agree to keep losing money forever. Either they find some loophole that does let them make money, or eventually you end up with abandoned property inhabited by people who can't or won't pay enough to actually maintain that property.

I've never owned rent-controlled property, but I did own a house which I kept empty for about a year instead of renting out. (Eventually I sold it.) Market rent wasn't enough to motivate me to do the work and take on the risks associated with having tenants. I know another guy who lives alone in a big two-family house for the same reasons. Some people who don't own property seem to think that renting it out is just free money, but things aren't that simple...

What's really fucked up is that selling a rental property doesn't incur the same tax penalties as selling a lived-in home. Should be the opposite. How ass-backwards can you get?