My (shallow) theory is that this is ONLY possible because they are startups and have no expectation/obligation in being profitable and a sustainable business. It's completely unaffordable for a standard company that pays it's bills on it's own revenues to compete.
My initial instinct is that if you get the best of the best covering most of the surface area of the company, it will naturally be successful almost independent of the original idea, due to the competitiveness of drying up your competitors, plus having innovation permeating at all levels.
The discussion I would like to encourage is if after X billions of dollars of funding, there's a point where a startup's success is pretty much guaranteed (at least in growth) and to what point OpenAI and Anthropic are a virtue of this.