Perhaps that page has simply not been kept up to date. The best way to find out would be to actually try to register it. I am certain you will not be able to.
Type "hotmail" into Google. You'll get a bunch of results with links. Type "hotmail" into the Go window. You get a specific log-in page immediately. Now type "google" into the Go window. Nothing.
This little experiment tells me that there must be some arrangement in place between NEOM and MSFT. It's the simplest explanation and it makes a lot of sense.