Bonkers roof profiles are primarily and American thing, to be honest; not that they’re totally non-existent elsewhere, but the super-complex roof on a detached house is very American.
tl;dr - It's driven by internal room shape requirements (plus weak planning; in some jurisdictions "no, that's an eyesore mess, redesign it" it a thing in planning, but I gather largely not in most US juristicitions).
