The calculations for these things must be along the lines of:
X: Do it ourselves - (relatively) modest number of subscribers x decent monthly fee
Y: Work with a partner - (relatively) large subscriber base x smaller monthly fee
If X > Y then do it yourself. If Y > X then take the money you're being offered assuming you get some good terms and a longish deal.
Whenever anyone asks why a major sports league (eg NFL in the US, EPL in the UK) doesn't go it alone and launch their own platform, it's usually because working with a partner or partners is much more beneficial.
Adam