New tenants have to pay market rate to begin renting. Rent control kicks in after that and prevents the rent from increasing much.

If the other renters had been there for many years, they'd effectively still be paying the market rate from years earlier. That can be a great deal less than market rate now.

That's why renters in rent-controlled units tend not to move as much - as market rates go up, your rent gets relatively cheaper over time and that's an incentive to stay put.

The rent is frontloaded. It averages out over the long run, but landlords charge more at the beginning of the lease to make up some of the difference caused by rent controls by the time the lease ends.

To me it’s more like if you have a non-rent controlled place you have to make it more attractive with lower prices, which is OK as you can just increase like hell after a year.

If you increase it, people can just move

Imagine: you’re in the middle of crunch time at work, your wife is pregnant, you receive some notice that the rent is going to increase ten folds in two weeks, good luck.

Imagine: you are a single techie living in SF, you get the notice and move to another apartment :D.

Why would you be single in sf

It wasn't that way when I shopped for an apartment in SF. (Summer 2008.)

The rent controlled landlords struggled, and didn't have much, or any, wiggle room for upkeep. (Just look at the Parkmerced saga. The place was a dump, but politics prevented them from fixing it.)

I moved into my rent controlled apartment because it was a good deal; the non-rent-control apartments actually cost more at the time.