Because instead of having 2 players that ask for 30% cut, having 6 that do the same is going to make Netflix any happier. There's no reason to think other similar platforms wouldn't charge the same. Look at GOG vs Steam, both charge 30% too, even tho GOG is much smaller market and for devs it means spending resources making the GOG version in addition to the Steam version, GOG still charges as much as Steam and doesn't see a reason to lower the cut.