Yah, that's what I'm saying. In those low periods they could just scale down the infra, but perhaps there's a constraint that doesn't allow for that. This lets them not waste it.
If they're running their own DC (or their own hardware in a colo) then I believe the only scaling down can by shutting down the systems at night, which, while non-trivial amount in electricity savings, is not really much when compared to the total hardware CapEx or even the total OpEx.
And, even then, you have to consider the cost of shutting down and bringing them up and the complexity it brings.
Now, if they're using a cloud provider they can theoretically terminate the instances. But, even in that case, to do that, they'll have to use on-demand instances rather than use reserved instances which will probably wipe out all the savings.
