Captain America: The First Avenger, he was so deeply changed by the incident that his return is more or less impossible. There will never be a team-up of Iron Man threats that includes Iron Monger, Whiplash, and Aldrich Killian, for example, nor will these villains act independently as none of them survived the movies that they were in.
Conversely, Mysterio, the main villain of Morbius.
The death of so many villains in the movies in which they first appeared has kept the Marvel universe closer to the real world - without constantly present threats, dangerous individuals seem to be more of a flash in the pan. With most of the Vulture's gang surviving With the Vulture among the best MCU villains in of sheer experience, there exists the very real possibility that Spider-Man's villains will gain actual practice in fighting superheroes. More importantly, since many of Spider-Man's surviving villains are looking to strike it rich instead of take over the world, they can be safely imprisoned rather than needing to be killed for the narrative.
In contrast, while many of the other MCU villains could have created recurring and consistent threats, their timely deaths prevented it. Without Whiplash and Iron Monger forcing Iron Man to share his technology with responsible agencies, the MCU hasn't normalized the kind of advanced technologies for agencies like SHIELD or SWORD that they have in the comics. Superheroes are exceptional, rather than a fact of life in the MCU - something that is slowly changing, in part because villains like Spider-Man's are now surviving with more regularity. They extend to other heroes; Vulture was as much an Iron Man nemesis as Spider-Man's, and had Tony Stark survived, Vulture might have shown up in a group like the Sinister Six to threaten the Avengers as a whole.
Throughout the first few phases of the MCU, a consistent line was that the world was changing. In some ways, it did - but an effort to keep it grounded in reality meant that villains that threatened the status quo died, and the kind of world shifts that their survival would have mandated didn't happen. Killian didn't maintain AIM, Hydra went underground with the disappearance of the Red Skull, and the Dark Elves, Destroyer, and Hela never made it to Earth. The world changed, but slowly - and now, with Spider-Man villains, including some from alternate realities, poised to take the spotlight, the world of the MCU might become more superheroic than ever.
