This piece, which I saw linked to on a Verge article, makes for interesting reading. Roku is still losing money because they sell the hardware so cheaply, but they're aggressive in their demands from channels because they have a dominant share of the streaming market:
In the UK, Roku would seem to be much smaller. They power Now TV boxes (Sky's streaming offering for cord-cutters/nevers, which is also providing the streaming technology that will seemingly power Peacock), but I reckon Amazon has the lion's share here. I don't think I've seen a TV with Roku built in either.