There doesn't need to be an explicit conspiracy. It only needs all the US frontier labs to be facing the same economic pressure (logarithmic improvement / $). It's a pretty obvious strategy - it's not like the large labs can magic up huge volumes of extra compute as demand comes online; there are almost certainly tweaking model performance to occupy the compute available and margin/cash burn targets.

That was one of the main points of the movie 'A Beautiful Mind' - that actors can coordinate without any explicit communication.