Avengers: Infinity War is considered by many to either be the best or second-best film that the MCU has ever produced, thanks to its insane ending and how it used the all-star cast well. While Avengers: Endgame fixed everything, fans were still left wondering how everything would turn out and it's clear that no one was disappointed. Both films were shot at around the same time so it won't surprise anyone that "Smart Hulk" was actually supposed to debut in Infinity War but was pushed back to Endgame.
Fans wondered why they didn't debut the character earlier after news of the scene was reported and we finally got an answer from writers Christopher Markus and Stephen McFeely, during the duo's live quarantine watch party with ComicBook.com. Markus stated that the scene just didn't work, even with Ruffalo working hard, as it had Banner and Hulk arguing for a good amount of time.
Considering how many stories Infinity War and Endgame had to cover, it's understandable that the transformation was never shown, though we would have still wanted to see it. Interested fans with money to spend can actually check the scene out if they buy the Infinity Saga Blu-Ray collection. Aside from collecting all of the MCU movies, it also has a number of never-released deleted scenes that any fan should check out.
If you haven't seen it yet or just miss watching the movie, Avengers: Infinity War is now available in digital stores. You can buy it on Blu-Ray too but don't go out of the house right now.