The point is to hit people with jaw-dropping opulence to get them into a frame of mind where they are small and they are dealing with something large. It is easier to convince them to do things they would not ordinarily do, and it makes them much more likely to see their host as important and able to provide unforeseeable opportunities.
Showing off is fun, but billionaires are canny and strategic people or they don't get to stay as billionaires. There are probably a few layers of thinking beyond being crass when pictures of their homes are pushed out into the public sphere.