Or because major American competitors do not compete on price, but rather on providing different features? Competing for low cost is not always a good idea, especially if you want to provide more services than bare bone hosting. The proof is on the scale, American corporation dominate market share internationally, and dwarf the likes of Hetzner. (not a dig against hetzner, I for sure would use them more than I'd use AWS if I was looking at building a budget conscious infra)
If anything, European operators have been utterly incompetent in that regard. And not for lack of trying. The only European players left are scaleway and ovh.
On the other hand, you can find tons of cheap operators in the US, they just don't get a similar rep to hetzner here on HN. Hetzner also found a very good niche with their second hand server that you can bid on, for sure. And to be clear, it provides a great service for the price.