The long version of the story is even funnier than that: apparently in testing the developers hadn't considered this a problem, because landlords' power is undercut if you mass-build low-rent social housing. However, lots of players chose not to do this and then were mystified when their cities became unliveable.
There are a fair few threads floating around Reddit and Steam Discussion which go something like:
Q: "Why do I constantly have these complaints that living costs are too expensive?"
A: "Rents are too high because of landlords. You need to build more low-cost housing."
Q: "But that'll ruin the aesthetic of my city! I don't want to do that! This is a bug, devs please fix."