I am willing to be you that a large number of Porsche owners are older senile men who just want s sports (or what they perceive to be a luxury) car and don't drive it in a sporty fashion at all.

Plus, I am sure there prospective buyers out there that would like a more fuel efficient Cayenne because they like the design, handling etc. and would welcome a diesel. All that matters is that the diesel engine delivers good fuel economy and has a sporty character. And diesel engines, despite most of them only revving up to 4,500 RPM can display a sporty character.