horsawlarway is correct regarding the nvidia shield. I'm not sure how much is nvidia, and how much is google in the "they". I kinda blame nvidia more than google (if I bought a google device I would expect google ads as part of the purchase), but it's hard for me to say. "they" the people who actually own the streaming device (nvidia shield) I "purchased" updated the software and added a lot of ads.

The ads showed up when the launcher got a major redesign, and the Google TV (or whatever they call it this week) launcher is a Google product. I seem to remember that nVidia delayed shipping the new enshittified version for quite a long time, so I'm pretty confident Google gets the blame here.