After he was beaten to a pulp by Thanos, Hulk went into hiding for all of Avengers: Infinity War, with fans somewhat disappointed in the way the Jade Giant was used. However, fans were also pleasantly surprised by how Hulk was used during Avengers: Endgame, which had Bruce Banner make peace with Hulk and become Professor Hulk. This was Hulk's body with Banner's personality and it made for some fun hijinks.
However, it turns out the writers originally planned to have Professor Hulk appear in Infinity War first, before the climactic battle in Wakanda.
Christopher Markus and Stephen McFeely told The New York Times that they planned to have Professor Hulk appear in Infinity War after Hulk's little crisis with Thanos. They even planned an arc for Banner in the film and would have included the scene where he splices his genes with Hulk and becomes Professor Hulk. However, that wasn't the case and things ended.
Though it would have been fun to see Professor Hulk in Infinity War, we can all agree that his appearance in Avengers: Endgame was great. The fact that he's a superhero accepted by the public was a nice touch and it's sad that he lost most of his arm when he brought everyone back with a good snap.
Avengers: Endgame is now showing in theaters.
Read: Chris Evans Spoiled Avengers: Endgame Before it Came Out and No One Noticed