With the finale of WandaVision now aired, some are upset and furious that their belief that Evan Peters was playing Fox’s version of Quicksilver in the show wasn’t validated. For weeks, even months, “scoopers” who get along by telling people what they want to hear have been leading people to believe he was 100% the Fox version of Quicksilver in the show and it would lead to Fox’s Mutants entering the MCU via the multiverse. However there’s a very good reason why that couldn’t happen; despite fans wanting it to.
I’ve explained it on the old podcast several times, but it all comes down to Hollywood politics, drama, and egos. Not to mention money. Allow me to use toys as an example. Prior to the MCU one of the reasons why you saw things like the Power Rangers-style Green Goblin in Spider-Man or a new design for a character compared to the comics all came down to money. In the film version of those characters, the producers would earn money from the merchandise of their versions of the character. As they created that specific version of the character, they were entitled to credit and money any time it was used.
A good example is how Zack Snyder created (and cast) the current DCEU versions of the Justice League characters. Which is why he receives an executive producer credit on any movies those characters appear in.
That brings us to the MCU and the Fox characters. Aside from likely wanting to avoid tainting the carefully crafted MCU with Fox’s continuity, if Feige were to bring in a character from the Singerverse, then people like Bryan Singer and Simon Kinberg would need to receive a producer credit (and likely money) in any MCU appearance for those characters. That’s also likely why Jamie Foxx’s Electro in Spider-Man: No Way Home is rumored to look different from the Amazing Spider-Man 2 version; he’ll be a different version of the character.
The fallout from WandaVision is one reason I’m glad I’m not involved with that stuff anymore. People only want to be told what they want to hear, not what’s really going on.