Because terms like broadcast tv, streaming and cable tv refer to the method of signal propagation, in other words OTA, internet, or using some sort of land cable. Not which channels are carried. Broadcast tv = OTA.
I can see why you are thinking like that. When we were younger broadcast and cable were each synonymous with a set of channels. Network tv was broadcast and CNN, etc were cable. But now I receive channels that I used to think of as cable - but via OTA!
I live in a rural part of Oregon. OTA tv signals are available here from a number of mountain top broadcast stations but they are all fairly far away, so my signal can be weak or intermittent. Lots of mountains here and line of sight often won't work - usually has to be a bounce. I use a signal amplifier, which is a small, inexpensive gadget that goes in between the antenna (a paper-thin sheet about a foot square) and the tv (or pc). Numerous good signals from several directions.