Screenwriters Christopher Markus and Stephen McFreely have stated that it was a challenge to write Infinity War for plenty of reasons. For one thing, they had a hard time working with the huge number of MacGuffins for the film. One thing that they have admitted was that it was hard enough to work with one MacGuffin. To have to deal with six of them brought forth a unique challenge for the screenwriters. They have eventually decided on what is known as a smash-and-grab approach for the film. Also, fans have noticed that Thanos already has one of the Infinity Stones at the start of the movie. For those that are looking for a reason, it is that the sequence that would’ve shown Thanos acquiring that stone would’ve done nothing to help the movie.
One other thing that the writers have revealed was that the original ending was much different. For one thing, the snap of the fingers was not meant for the ending of Infinity War. It was originally going to be saved for the next film. The original ending would’ve made it feel like too much of a cliffhanger. Therefore, the snap was moved to the end of Infinity War so that the film could feel like its own complete film. Avengers 4 is going to explore the consequences of the snap.
Had they gone with the original plan, the film wouldn’t have been anywhere near as good as the one that was released. Even though the film would’ve likely been a good film, it would not have had the effect that the final version had on the audience. Infinity War has turned out to be one complete emotional journey with the next film looking to be another complete emotional journey.