The problem is simple: in a perfect society we wouldn't increase flat prices simply so a landlord can make even more profit. There is no actual, logical reason why the flat should cost 5x as much, only made up ones that basically say "but I wanna!". There's no actual 5x increase in costs for the landlord, they pocket most of that additional rent.
Living space isn't something you should be able to profit this heavily from in a functioning society, as it's a basic necessity to life. It's alright that nicer flats cost more but nowadays we value huge additional profits to landlords higher than basic human rights, provocatively spoken.
Here's the full set of measures recommended: