story in the Marvel Cinematic Universe (MCU) is a little scattered, but I'm glad Marvel discarded one part of his arc that was set up early on. Hulk is one of the original Avengers in the MCU, and while Mark Ruffalo made his debut in that 2012 movie, the character was introduced earlier in 2008, just a short time after Iron Man came out. But despite appearing so early on, Hulk's story got lost in the background of the MCU.
While the Hulk hasn't had a solo movie since 2008, and that felt like a very different iteration of the character with Edward Norton in the hot seat, Hulk pops up in a lot of other projects. With that, Hulk's story tends to jump from one moment to the next, with very little explanation or exploration in between. And due to this scattered approach, it with Black Widow.
In 2012, The Avengers followed the formation of Earth's Mightiest Heroes into a formidable team. While Iron Man, Captain America and Thor all had earlier stories outlining the lead up to this film, the from the 2008 film. Likewise, Natasha Romanoff, a deadly assassin working with SHIELD, had small hints of a story introduced in movies like Iron Man 2, but the character was largely a mystery.

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With both characters feeling like outsiders, and containing intense anger and aggression that wasn't always in their control, Nat and Bruce felt some sparks of connection. With clear electric energy bubbling between them, it seemed like their story was inevitably heading towards a romance plot. However, despite their connection, and , their story never really went anywhere.
With the expanse of the Marvel Cinematic Universe sprawling out and featuring dozens of heroes with their own individual stories, Marvel had to be more selective about the stories they put time and effort into. And for a character like Hulk, whose story was only ever progressing between films or in the background of another character's movie, it made establishing his narrative a challenge. Aside from minor cameos, Hulk's next big appearance was in Avengers: Age of Ultron, where the .
However, by the time Avengers: Infinity War came out, the sparks seem to have fizzled out. And ultimately, considering the fact that Hulk made some more notable appearances in movies like Thor: Ragnarok, which explained that he'd been trapped on that planet in his Hulk form for an undisclosed amount of time, it makes sense that in the MCU.
Considering the fact that between Bruce Banner and Natasha Romanoff they got a grand total of two movies 13 years apart, it makes sense that their romance was ultimately cut from the MCU., or explore how their connection changed the dynamics of the team, or how they changed as individuals. And with both of their solo movies, it was much more focused on providing a story that was disconnected from the wider Avengers.

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If Marvel had tried to push the romance plot, it would have felt rushed and underdeveloped. Nat and Bruce's connection may have felt unearned, and it would have taken time away from more pivotal parts of the stories where they appeared. Instead, we got some sparks flying, some longing looks, and an acceptance that their relationship was never meant to be. And honestly, that did a lot more for story in the than if he and Nat had a relationship that went nowhere.