Part of the reason is that at the scale of a country like the US, if you are going to have several supercomputers build in the coming years, you want to diversi

Part of the reason is that at the scale of a country like the US, if you are going to have several supercomputers build in the coming years, you want to diversify to avoid putting all your eggs in the same basket (and to giving a preferential treatment to a single vendor). So, as long as they can get a given set of applications to run above a given performance threshold, alternative vendors have a shot.