People simply prefer the SUVs. They ride higher, people like that elevated feeling. They also give the added space, which is a selling point. They are undeniably trendy, and gas is super cheap, 2.20 per gallon here, so not high at all historically.
So that together with the higher ride height, which makes getting kids in and out easier and almost no extra cost makes the SUV more likely to win than a similarly specced estate.
(and please keep in mind a "SUV" in Europe is not really the same as "SUV" in the states).
SUVs are a comfortable ride. You see everything, you sit comfortable, they feel spacious (not always are...), it's the design between normal cars and pickup trucks or vans.
Still people buy more and more SUVs