If you want to talk legality etc., most contracts have a "force majeur" clause that would cover this sort of thing. And even if it didn't, if enough businesses start having to modify or break service agreements in these ways through a world-wide crisis then governments will step in and legislate them out of liability. There won't be too much sympathy for the "victims" of Netflix either. Not from the general public, especially those who lose friends or family to the pandemic. Not over someone's pixelated experience of End Game or The Office. I know people who are sick, one closely, and I don't know if they're going to survive. Suffering through SD quality (or worse!) isn't what I concern myself with at the moment.
There is absolutely no legal reason to downgrade performance of service. It's a big WTF.
What's next. A guy telling other to sell lesser quality of what?