A big part of the reason banks are more conservative than landlords is because it takes about two months to evict a tenant, and about 18 months to foreclose on a borrower.

Landlords and lenders are not weighing the same risk, at all.

So it's not entirely fair to suggest that banks are saying renters "can't" afford a mortgage payment lower than their rent payment. It's more like, "as a lender, I am not willing to bet 18 months worth of payments, plus all the costs and hassle of a foreclosure, that you will be able to make this payment."