Worry about the leg-thick power cable not the pinky-thin fiber. The cost of the fiber itself basically doesn't matter relative to a data center itself.

I see that you know nothing about anything involved. The cost of cable is essentially irrelevant in both cases, the "everything else" is the expensive part.

Power can be had from the closest high voltage line (and maybe even easier to get outside of the city)

The fiber have to be dragged from either nearest point of presence (a building with many fiber connections coming to it from multiple companies to exchange traffic), or to whatever dark fiber infrastructure is available nearby.

In city, that's usually not that hard, ISPs already "plumbed" most of the bigger cities with fiber infrastructure.

Middle of the boonies, where we want the datacenters to go ? Dig, dig dig, get permissions for digging, get permission from everything around the ride from city's fiber infrastructure to the place in middle of nowhere, months or years in getting permissions, and red tape anywhere. There is probably some power close enough, or at the very least you can find a location close to power, but location close to fiber will if anything be some existing industrial centre, and even that might not be a sure bet. You might get lucky and get a permission to use existing poles to drag some fiber on them, but it's still PITA

They are talking gigawatt. That pretty much implies dedicated long-distance transmission lines. The 1.4 GW they mention are very close to the full output of three mile island. This is not a small power situation that is done with existing power lines. And the moment you drag power in from 20+ miles away, you might as well just put fiber in there as it seems very easy given by how prevalent it is for long distance lines these past decade or two.