Because of this, it might be unclear exactly what a rival power is doing with all that heat and power and all those chips, but it's very easy to know that they're doing something. And, therefore, very easy to know when you're "ahead", in terms of nowhere else on Earth showing the right MASINT signature to represent the same compute capacity you have.
Mind you, this is commutative; the Russians, Chinese, and other powers with satellite networks can take the same infrared imagery, and do the same maths, to calculate exactly how much more compute the NSA has than they do; and their OPSEC doctrine is necessarily designed around this knowledge.