That's not really true. Rent to income ratio varies quite a lot
Data from US gov since 2000 show this (BLS, SSA), as do multiple university studies (MN, KY). And the ratio for rural areas is getting worse, more pressure, than urban.
That it varies is not interesting, lots of things have variance. The data shows its generally true.
Income to rent ratio, which is what this thread is about, varies geographically. Rent eats 30-40% of income in prestige cities like NYC or SF or LA. It's only 25% in Kansas City or Columbus.
You seem to be thinking about overall cost burden over time.