If you have Sky Movies you can get Paramount+ too.I currently have Disney, Netflix and HBO bundled into my Sky subscription. There's clearly a benefit (more subscribers) and that's the key.
If as a standalone platform I can only get 50,000 subscribers and another platform can get 70,000 then why would I not seek a partnership that bundles my platform with the other & offer that bundle at slightly cheaper price than 2 separate ones? If we agree we both end up with 120,000 subscribers. (best case)