So it appears I'm telling you what you already know, but anyway: Roku sells hardware for around cost, and makes money on advertisements and carriage deals. If ads on the home screen are a big deal, then Apple TV might be a preferable streaming platform. Traditional TV providers (Cable, Dish etc.) may also offer devices without ads, though commonly with monthly fees. I don't recall seeing any ads on my Dish Network receiver.
Basically everyone wants to make some money, some companies just do it by charging you enough to make "reasonable" profit, and some get someone else (advertiser) to pay so you can pay less.
It seems to me that most people in the US really like the pay little and get ads business model, because those business models are very common. I dislike ads myself, though primarily the ones in TV shows that interrupt the flow and waste time - I can't watch The Roku Channel at all, for example. However, Roku's home screen ads have not bugged me, so far at least. So, a Roku with ad-free TV subscriptions works well for me.