> More power than anything* the fibre usually comes later.

This depends a lot on the datacenter. Some are sited specifically around proximity to existing fiber, or more especially proximity to places where multiple fiber backbones intersect (e.g. carrier hotels / meet-me-rooms). There's a datacenter going up here in Reno to that exact effect, with a lot of the public complaints being “but why do we need a datacenter in the middle of town?” even though:

1) that's where multiple fiber backbones intersect

2) it's being built in a mixed commercial/industrial zone with other datacenters already there

3) the company building it has another datacenter dead smack in the middle of Downtown doing similar carrier hotel stuff, and the new one is an extension of that