The trope of video/audio breaking down into static is an easy shorthand that is unlikely to be forgotten, probably even well after all the devices capable of doing so have long since been buried in the landfill.
It’s especially hilarious in media depicting the far-flung future, where apparently all technologically advanced space men and their communications devices – not to mention high powered central supercomputers and so on and so forth – somehow still work over NTSC television signals. Even by the early 1980’s it should have been entirely predictable that in “the future” anything like that would be digital, considering we already had widespread digital audio media (CD’s), and digital video was already making inroads into the computing industry.
This is exactly why. Preventing screen burn-in may be a tiny peripheral reason also, but providing a familiar experience to chronically myopic and cranky users (i.e. boomers) is probably the bigger one.