I think it's funny that the producers try to play up the "tension" between Hilary and David, when it's clear they are BY FAR the nicest people on the show, and actually seem to respect each other, unlike some of the bobo homeowners.
My theory on why many of the homeowners don't give Hilary more money is because cash loans are more difficult to come by than larger mortgages, right? Like, if the show guarantees them $10K in cash towards either the repairs or the new mortgage, the money goes farther towards a higher home price tag than it does as cash...I think.