Not only is it cheaper to build a new datacenter than to retrofit a 30 year old building. It's even cheaper to build your own power company next door.
What's the basis for that belief? Sure, if you're speaking of the largest data centers in the world, with rather low margins which cooling costs can cut into, then you have considerable incentive to come up with ways to reduce that. Simultaneously, you have huge economies of scale while simultaneous swamping the local energy providers.
But if you're a small IT department providing a high value product (say, making sure a company's servers work is far more important than shaving dollars off of PUE), then the incentive to play the PUE game isn't there. Nor are the benefits.
Unless you think funneling a few megawatts through 80 year old cities is cheap.
If you're in an urban environment, then the infrastructure is there to provide a lot of cheap megawatts - at least outside of California which is special.