; Date: April 17, 2019
The FCC enforcement advisory (embedded below) is pretty clear about what's going on.
There is an increase in devices described as "Video Set-Top Boxes" that primarily stream internet content. And yes there is a variety of these things, like the Apple TV, or Roku, or Chromecast boxes, and many more.
Where the FCC comes in is these devices include WiFi transmitters. WiFi transmitters must comply with FCC regulations, Part 2 and Part 15.
To comply with the regulations, the device must be "authorized" through a certification process. Further the device must be labeled with a valid FCC Identifier. And the device must say clearly it complies with FCC regulations.
It seems that some of these devices do not comply.
I can just imagine some hardware hacker in his garage starting with the Raspberry Pi Zero W board design -- it's an open source thing and anyone could take that design to create a new board -- and coming up with a streaming media device. Perhaps they'd use the Kodi client for the software? And then thinking that since the device uses standard WiFi chips there's nothing further to do.
But of course the FCC has other ideas in mind, meaning that path to market just described does not involve the required certification in order to get the FCC identifier for that device.