I am doubting myself now after not being able to quickly find a verified source but I've worked with lots of smart TVs and seem to recall Samsung or LG models using this simulated effect. It would have had to have been simulated since there was no signal coming in, and I recall the pattern being noticably pseudo random.
As for why: I have no idea! Maybe just for user familiarity reasons, since a lot of people grew up with that kind of analog feedback that the antenna wasn't getting a signal.
Take what I said with a grain of salt, though, since like I said I wasn't able to quickly verify it. It's a vivid but ambiguous memory, though, since I also thought it was strange