A lot of DoubleTrees seem to conversions from something else. (At least, a lot of the DoubleTrees I've seen being announced in the Hilton forums new openings thread over the past few years.)
But in this case, the Quality Suites went through several other lives before it became the Hyatt House (which seems to have a full kitchens in each room).
And the one Quality Suites I'm familiar with (the one near SNA) does not have a kitchen in each room at all (in most rooms, anyway), so I'm not sure what the path was from that particular Quality Suites to Hyatt House.
(Quality Suites is a bit different than Quality Inn, in the styles of the rooms, but based on the one I've seen it's simply a suite in the sense of multiple rooms, a la Embassy Suites, not a suite in the sense of having kitchen facilities in each room, a la Candlewood Suites.)