> If their tenant goes out of business, they're not getting the back rent and now they'll have a vacancy in a time they're unlikely to find another tenant quickly.
In some cases (I have first hand experience - perhaps it is limited to small businesses), the business owner has to agree to be personally liable (with his/her own personal assets) if the business fails to pay the rent. The business may go bankrupt, but the landlord can still go after the owner's personal assets.
That's one way for the landlord to lower his/her risk exposure.