We can speculate all we like, but I think it's worth noting that we have no idea how many people actually buy and use pirate TV boxes. Remember that at the height of the satellite piracy hysteria a few years back, estimates were around 2 million pirates in Canada and the US combined. That's a big number, but a relatively tiny percentage of TV subscribers.
Personally, I don't actually know anyone subscribing to these services. I do know some people who pirate TV and movies, but they do it the same way they've been doing it for years, and they wouldn't start paying for a pirate feed. Are lots of people subscribing to these things? Almost certainly. But I don't know if lots is tens of thousands, thousands, or just hundreds.
Ultimately, the way to turn the pirates back into legitimate customers, and the way to keep legitimate customers from becoming pirates, is to put out a good product. The music industry has proven this for us. When the music industry told people that the only way they could get songs was to buy a whole album for $25 which includes a bunch of songs they didn't want in a format they didn't want, they said screw this and downloaded the one song they actually wanted for free. When iTunes came along and offered people the chance to buy a single song for a dollar and have it delivered instantly in a format that worked for them, people started doing that. When music streaming services came along and made it all even easier, even more people went that way.
There have been other successes in this model, TV-wise (MLB.tv, Hulu, etc), but Netflix is the only one to be really ubiquitous. Why is Netflix the only one to really work so far? They get it all right. They have content people want to watch, they let them watch it in they way they want (they have great apps on almost every platform), and they offer it at a fair price. That's why almost nobody pirates Netflix shows.
Cable TV has the content that people want to watch, but that's where it ends. They make you watch it on their platform (TV boxes) with their bad interfaces, with commercials, and at the time that they choose to air it. And they charge you a high price for the privilege. Where they have attempted to release internet based products to meet that customer desire, they have inevitably been some combination of low quality streams, unreliable, crippled by bad interfaces, or extremely limited in platform support. Eventually, cable TV will have to figure it out or be devoured by other companies who do. It sounds like Google and Apple are finally getting in the game now, so they may be running out of time.