WARNING: The following contains major spoilers for Spider-Man: No Way Home, now playing in theaters.
Spider-Man: No Way Home was riddled with theories even before the film was released, but despite all the speculations, the film managed to deliver some great twists. One of the twists was also a heartbreaking one, as Aunt May was killed by Green Goblin. No Way Home used this opportunity to give Tom Holland's iteration of Spider-Man the speech about great power equaling great responsibility, which was previously absent from the Marvel Cinematic Universe and associated with Uncle Ben.
A Reddit theory by Pietin11 suggests Uncle Ben's MCU death had nothing to do with Peter, which is why it has taken so long for him to hear the iconic speech about responsibility. The theory suggests that Uncle Ben was killed during the Battle of New York, making him collateral damage in Loki's invasion. This would mean that Peter was bitten after Uncle Ben died, which would then explain why Peter didn't get his speech when he became Spider-Man.
The theory goes on to suggest the delay in Peter learning that important lesson would explain some of his reckless behavior in the MCU, like giving E.D.I.T.H. to Mysterio in Spider-Man: Far From Home without a more thorough background check or consulting with anyone else. Another example is trying to use magic to solve his friends' concerns about college instead of talking to the admissions board.
Peter in the MCU uses his powers undeniably with good intentions, though he does end up being a little reckless and a bit cavalier with the true scope of his abilities. If Uncle Ben died during the Battle of New York, it would have happened far enough removed from Peter getting his powers that Peter would still be sad, but the initial mourning process would have passed, and this lesson wouldn't have impacted how he acted as Spider-Man.
Uncle Ben's death is cited as a reason why Peter didn't tell Aunt May that he was Spider-Man in the first place. Peter tells Ned in Spider-Man: Homecoming that after everything May has been through, he can't add his powers to her burdens. So that would explain why Peter didn't get the responsibility lesson from her sooner. By the time she figured it out, it wasn't long after that she and Peter were snapped away. This turned Peter's iconic lesson about responsibility away from a five-minute origin story into a multiple film character arc.
While this theory makes a lot of sense, there just isn't enough evidence within the MCU to confirm its validity. Uncle Ben could've just as easily died in a car accident, had heart attack or really any other reason either before or after Peter became Spider-Man, and the same evidence listed in the theory would still apply.
However, even if the theory can't be explicitly confirmed, it is compelling. No Way Home ends with Peter Parker living alone, poor and without a support system in New York City, committing to being the friendly neighborhood protector we all know and love. Essentially, the MCU turned Spider-Man's typically brief origin story into a six film epic queuing up any potential sequels to follow in the steps more similar to the films that have come previously. The theory may not be confirmed canon, but it does fit into the MCU's version of Spider-Man by saying that Uncle Ben's death was not Peter's fault.
See if this new theory aligns with the latest Spider-Man film, No Way Home.