Bezos also has a rocket company. Plus there's Richard Branson. And others.. And then you have private jet travel, massive mega yachts, and countless other extravagances. For a certain class of billionaire, having a private rocket company is a vanity project. These rocket companies are vanity projects by rich sci fi nerds. Yes, they've done some really good technical work, but they're only possible because their founders were willing to sink billions into them even without any proof they'll make a profit.

What you are missing is that as people's wealth increases, their resource use just keeps going up and up and up. To the point where when people are wealthy enough, they're using orders of magnitude more energy and resources than the average citizen of even developed countries. Billionaires have enough wealth that they can fly rockets just because they think they're cool, even if they have no real path to profitability.

And no, the hypothetical of the robot skyscrapers is not "meaningless." You just have a poor imagination. To have that type of world we only need one thing - a robot that can build a copy of itself from raw materials, or a series of robots that can collectively reproduce themselves from raw materials gathered in the environment. Once you have self-replicating robots, it becomes very easy to scale up to that kind of consumption on a broad scale. If you have self-replicating robots, the only real limit to the total number you can have on the planet is the total amount of sunlight available to power all of them.

The real point isn't the specific examples I gave. The point, which you are missing entirely, is that total resource use is a function of wealth and technological capability. Raw population has very little impact on it. If our automation gets a lot better, or something else makes us much wealthier, we would see vast increases in total resource use even if our population was cut in half.