If I had to guess these are used for urgent video transcodes. New uploads to popular channels and on-demand transcoding. I suspect that CPUs are still often use

If I had to guess these are used for urgent video transcodes. New uploads to popular channels and on-demand transcoding. I suspect that CPUs are still often used for background batch encoding. But maybe 20x is enough that the power cost of extra CPU usage isn't worth it and they will do it all in hardware.