I think because the term "SUV" sounded more robust and widened the purchasing audience than the former "mini-van" which marketed to families. "SUV" not only fits "families" but also the single, not married group who want something that sounds more "sporty" than just a "family" vehicle, to the old dude thats now going through their second childhood! (like me). SUV sounds kind of sporty and rugged, appealing to anyone, including the "family" car.
Basically... it's all words anyway. Call it a "toad monster" if you want. It doesn't change what the vehicle actually is. But, how many people would actually buy it, if it were actually called a "toad monster"?