"why not take it from the truly "useless" industries like entertainment, cosmetics, toys, or luxury cars"

I couldn't be more pro-Billionaire Astronauts, but at the same time there is danger in them spending their money and influence on things that may not work.

If they had gone out and bought more cars, yachts, and real estate, that's money that goes into mature industries with efficient supply chains that support the livelihoods of many people.

You can look at a billion dollar yacht and say, "What a waste", but the shipwrights, plumbers, electricians, carpenters, and welders who built the yacht, not to mention the crew that steers, maintains, and cleans it probably don't think it was a waste, nor do the people who work in the industries that provide the materials for it.