Recalling old cable rules.....
OK, I'm an old fart and my memory might be a bit fuzzy, but perhaps this really becomes an FCC issue?
As I recall (and I admit it's kind of fuzzy) in the early days of cable TV, you paid the company to come out, and hook up a TV set to cable, and you paid for channels. If you wanted a second, third, or more sets connected, you had to call the cable company, pay an installation charge for each additional set, AND pay an additional monthly charge for each additional set.
Then, the FCC changed the rules so consumers were allowed to hook up whatever the heck they wanted to their cable, and were not required to hire the cable company to do it (and suddenly cable, splitters, connectors, etc became available in local stores) AND they could no longer charge for signal going to the additional sets.
So, isn't the ability to stream to a device in your own home, the signal you are already paying for in this same category, just with a different technology? How about all those "Rabbit TV" transmitters you could buy, that let you plug in your cable to the unit, then put matching Rabbit receivers on sets in your house so you could watch cable TV anywhere in the house without having to run physical cable? This was basically the same thing -- re-transmitting the cable signal within your house. This was legal, and popular for many years.
There may be a few hazy details here but that's how I recall it all going down in the cable biz in the late 70's in Minneapolis, anyway.