Why don't landlords consider our household income?

We're looking for a new place. Married. Both work full time. He is a student (no loans) but, we do not disclose that. Make about the same income each. No children. Why is it when seeking approval for rent agencies only look at our individual incomes like we're just room mates? The place I want is just under 40 percent my gross but when considering our household income it's less than 20. I don't think that's unreasonable. Neither of us have debt. We've got some savings and I have plenty of credit available in case of a short term cash flow issue which isn't even likely our jobs are steady.

I'd like to find a unit I won't mind living in for the next 5 years or so unless a career change brings me across the country or overseas. I'd rather not settle then find myself moving again in a year when I don't need to.

Buying is too long term and not something I want to deal with right now. I've seen too many people go broke trying to sell their homes or stay put when there are opportunities because they can't sell without losing money. I like the freedom of knowing I could pack up next month without worry. Sure, I'd have to find another renter to take over a lease but like that is hard in a city with a "rental shortage" and I do not like private landlords because I don't feel like they would respect my privacy.I've rented private before and found it obnoxious.