I'm not sure what you used to calculate it, but it definitely isn't only "expensive cities with inherited properties"... I did the math on the last house I rented: lived there for 8 years. It was a duplex in a city in a very cheap cost of living state. Just my rent alone for those 8 years more than covered what the entire duplex was purchased for 3 years prior to me moving in. That means if both sides were occupied, which it was for all but 1 month in the 8 years I was there, it's paid for in full in 4 years. Even if you "have to renovate" in 30 years, hell even 15 years, you have 10 years of pure profit even after considering insurance and property taxes and probably even maintenence costs...

Maybe your area doesn't have high demand for rentals or you under-valued your rent price, but there wouldn't be so many people doing it if it wasn't profitable.