> Sf’s rent control also means tenants can’t leave

They have exactly as much freedom to leave as they would without rent control. They _choose_ to stay because rent control has made it advantageous to stay. The way you phrased it implies you're suggesting this is a bad thing for renters but that is strictly a positive. Without rent control they'd have zero affordable options, with rent control they have 1 affordable option. Woe to the inhabitants of rent controlled apartments with their golden handcuffs.