Avengers: Infinity War, and eventually discovers the Soul Stone on Vormir, guarded by a hooded and sorry-for-himself Red Skull. Obtaining the Soul Stone requires a sacrifice, and Thanos tearfully offers his daughter Gamora in exchange. Unbeknownst to the Mad Titan, Gamora's soul becomes one with the stone, and after completing his snap, Thanos is confronted by a young Gamora in the Soul Word, where he its his ambition cost "everything."
Other Soul World scenes were originally included alongside the two snaps in Avengers: Endgame, but both were ultimately cut from the finished film. The Russo brothers got as far as shooting a Tony Stark Soul World sequence, in which he was confronted by an older version of his daughter. Fans are split on whether the scene would've improved Iron Man's MCU ending or distracted from the impact of his death, but the moment was cut regardless after faring poorly during test screenings. The other Avenger to snap the Infinity Gauntlet is Hulk, who also would've experienced a journey to the Soul World in the original Avengers: Endgame plan. According to the film's writers, Christopher Markus and Stephen McFeely, Hulk's snap would've taken him to meet... Bruce Banner.
While the jury's still out on Tony Stark's Soul World trip, the Hulk and Bruce Banner conversation would've surely proved detrimental to the green professor's MCU story. Thanos and Tony Stark meeting their daughters not only feels natural, but also continues the parallel between Iron Man and Josh Brolin's villain. It was Gamora who Thanos sacrificed in order to complete his bejeweled glove, and Stark undoubtedly would've been thinking of Morgan during his final moments. Short of recalling Liv Tyler to reprise her role as Betty Ross or reigniting Banner's aborted romance with Black Widow, Banner has no loved ones for the Soul Stone to conjure. Bruce speaking to Hulk feels somewhat redundant. They didn't exactly share the same dynamic as Thanos and Gamora or Stark and Morgan, nor is there any thematic reason for Hulk and Banner to talk after snapping the world back to life.
The only reason Bruce Banner and Hulk might have a heart-to-heart is to resolve the eternal conflict between them. For most of his MCU tenure, Banner is waging a mental war against Hulk, and the two personalities meeting in the Soul World could've laid that hostility to rest... but Avengers: Endgame already achieves this with the Professor Hulk character. Following Avengers: Endgame's 5-year time skip, Hulk attains a harmonious balance between his two personalities. The inter-character conflict was already over, and Banner emerged victorious by blending his genius scientific intellect with Hulk's near-unrivaled strength. After Banner made friends with his Hulk, the significance of them meeting inside the Soul World would be lost. They might as well chat about the weather, or the obvious sexual tension between Rhodey and Carol Danvers.
Thanos encountering Gamora compliments the big purple villain, adding a layer of emotion and humanity that would seldom reveal itself in the real world. Tony Stark being able to see his daughter as an adult before dying also resonates on an emotional level, affording the character a goodbye he otherwise wouldn't have experienced. But Hulk meeting Bruce Banner in the Soul World only weakens the resolution of the MCU's Professor Hulk reveal, while contradicting Banner's claim that the two sides had found peace. Avengers: Endgame is a better film without it.
