Allow me to present two pictures (and again, let me acknowledge the people at IPUMS for making it easy to use census and American Community Survey Data). The first is median rent to median renter income for about 225 MSAs in 2000.
The next is the same picture, but for 2016.
Notice how in 2000, in the vast majority of MSAs, the median renter would spend less than 30 percent of income on the median rental unit. By 2016, that had reversed: the median income renter pays more than 30 percent of income in rent in the majority of cities. And while the 30 percent number is somewhat arbitrary, that fact that rents relative to incomes rose nearly everywhere is not. It is easy to see why renters are upset.