I actually agree that those raids would be fun, it's the context that matters here though. If Blizzard is already known for being lazy and having a weak and poor content cadence, then the last thing they should do is rehash old raids. That's another feature that really only works if the team is in good standing with the players.
That aside I'd even argue though that you can't really even do those raids until they get timewalking into a better place. A small event that happens every other week for limited dungeons just sucks. They need to find a way to encourage players to engage with the 8 expansions worth of dungeons and raids they've released over the years. Once they've solidified a way for that to work, and get it working well, then they can start doing MC Rag Ultimate or whatever.
I agree, they do need more content. End of conversation. The covid excuse is an old and tired one for an industry that's almost entirely digital these days. And they most certainly haven't been managed well since Legion. I still don't understand why Legion had so much content and everything else has sucked. Was it really just WoD being cut? Seems like there's more going on there than just that but who knows? I'm not privy to the internal workings of Blizzard.