When we first see Thanos in “Infinity War,” he has just destroyed the Asgardian ship carrying the last remaining survivors of the planet’s destruction from “Thor: Ragnarok” as he searched for the Space Stone — which Loki had stolen from Odin’s vault. In one impactful opening scene, the Mad Titan easily overpowers Thor and even defeats Hulk in a fistfight thanks to the Power Stone.
We don’t see how Thanos obtained the Power Stone, which was last seen on Xandar at the end of the first “Guardians of the Galaxy,” but it seems based on Jim Starlin’s comments that we could have seen a rather lengthy and epic battle wherein Thanos would get the stone (presumably after destroying much of the planet).
This is not the first time we hear of deleted scenes centered around Thanos. “Infinity War” screenwriters Christopher Markus and Stephen McFeely originally envisioned the film as partly a Thanos origin story, and several scenes with flashbacks to Thanos’ youth were written before getting ultimately cut.
A movie framed around the villain, perhaps one with Thanos narrating the story a la “GoodFellas” could be interesting, sure, but this is already one mighty long film, and to add another 45 minutes to what is essentially just another one of five McGuffins would have been excessive.