I don't know the details, but large personal residences tax your brain (as well as your bank account).

Instead of spending hours of his life negotiating RE purchases, maintaining his properties, cutting checks to plumbers, doing renovations, etc. (that I hear many other billionaires do), he was practical with his (luxury) purchases focusing on time saving (living near work, fast food, private jet) and the experience (luxury vacation).

If you don't appreciate that, I think you're missing the point of his frugality.