Overall, Marvel has had a pretty poor run of villains, but Hugo Weaving was perfectly cast as Red Skull in Captain America: The First Avenger. He had the perfect balance of menace while staying in the realm of old-fashioned villainy to make his mark as Cap's longtime nemesis. Since the character didn't die so much as getting beamed up at the end of First Avenger, fans assumed they'd be seeing him again some day, and they were right. The character returned as the guide to the Soul Stone in Avengers: Infinity War and Avengers: Endgame, but this time he was played by Ross Marquand.

Speaking to Time Out, Weaving explained why he wanted to return to play Red Skull, but ultimately decided against it:

‘Oh, yeah. I loved playing that character Red Skull – it was a lot of fun. We were all obliged to sign up for three pictures: I was thinking [Red Skull] probably wouldn’t come back in “Captain America” but he may well come back as a villain in “The Avengers”. By then, they’d pushed back on the contracts that we agreed on and so the money they offered me for “The Avengers” was much less than I got for the very first one, and this was for two films. And the promise when we first signed the contracts was that the money would grow each time. They said: “It’s just a voice job, it’s not a big deal”. I actually found negotiating with them through my agent impossible. And I didn’t really wanna do it that much. But I would have done it.’

For starters, it's not really a voice job, is it? Unless Red Skull was completely CGI (and he didn't appear to be), then you've got to get in the makeup chair for a few hours every day of filming. And furthermore, he's Hugo Weaving and you're Marvel Studios. You can afford to pay this man slightly more money if for no other reason than you needed him back in 2011 before every Marvel movie was a guaranteed hit.

As for why he's not coming back for Matrix 4, that sounds more like a scheduling issue:

‘“The Matrix” is a very different story. It’s unfortunate but actually I had this offer [for “The Visit”] and then the offer came from “The Matrix”, so I knew it was happening but I didn’t have dates. I thought [I] could do both and it took eight weeks to work out that the dates would work – I held off on accepting [a role in “The Visit” during that time]. I was in touch with [director] Lana Wachowski, but in the end she decided that the dates weren’t going to work. So we’d sorted the dates and then she sort of changed her mind. They’re pushing on ahead without me.’

This is all kind of unfortunate because Weaving's a delightful actor, but I'm kind of okay with him not returning for a new Matrix. However you feel about Matrix Reloaded and Matrix Revolutions, Agent Smith is the primary antagonist. If you bring him back again, it diminishes the victories our heroes scored in those movies.