Uber's spending was directly attributed to growth. They were launching in new countries, new cities, new markets every day, and that required burning through an immense amount of money. Of course that growth didn't need to last forever, and once the service was fairly established everywhere the spending stopped.

OpenAI on the other hand has to spend billions to train every new iteration of their model and still loses money on every query you make. They can't scale their way out of the problem – scaling will only make it worse. They are counting on (1) the price of GPUs to come down in the near term or (2) the development of AGI, and neither of these may realistically happen.

Uber was a literally life-changing product with an obvious value for anyone. LLMs have neither benefit.