The ultra rich want an SUV to go with their supercars. Only Range Rover was available until the Germans stepped in. Only makes sense for Jaguar, Bentley, Aston Martin to do the same.
Like it or not, SUVs sells, especially in USA. That's why we have so many "crossovers" on the road, so many Klugers, Jeeps, Mazda CX-whatever, etc. It's just the way people buy cars now.
Funnily enough, my Liberty has more interior space than those huge Jeep SRT whatever they are.