Low Price to Rent: Why do people rent?

[Daniel Lehrman]

I'm looking into investing in areas with low price-to-rent ratios, like Metro-Detroit.  I've asked a few PMs this question, but I don't get very good answers:

What is the fundamental reason that price-to-rent is so low? 

Some answers I've gotten: 

"Section 8 housing inflates rental rates"

"Tenants can't get approved for a mortgage"

"Tenants are uneducated"

Though all true, these reasons seem to only partially answer the question.   Can someone provide some insight?