Because the have their own on demand service. Most of the items on Movies Now's latest releases are also on Sky Box Office.
Why continually broadcast 50 streams across their backbone network when they can perform the delivery on demand?
Why duplicate content? Why pay Sky anything for a service they can provide themselves.
If it where to go ahead any Sky Box Office deal is going to be a branding exercise with Tiscali providing the network and on deamnd infrastructure and Sky providing the rights, material and branding.