This is exactly the model of the Roku - it started out as a Netflix Player, but realized that deals with other content providers would be key, and that other Netflix platforms may not want to compete with a Netflix-provided player, and so Netflix spun it off.
It's a $1.5B company now (not monopolistic/huge, but a nice business...)
Imagine if Apple bought Intel. It would be extremely likely that Intel would be forced to continue to sell its products to everyone, even if theoretically Apple might want to just stop shipping the parts to competitors.