Affordable housing is actually quite scarce inside the city right now, people on average don't really earn that much. The rent controls had no actual effect on price increases. It has been suggested that the rules are simply being ignored and most tenants won't pick a legal fight with their landlords when housing is so scarce:
https://www.welt.de/finanzen/immobilien/article150877146/Die...
There's more than enough housing for higher-income people, so rent control there is moot.