We had seen first seen Thanos in the mid-credit scenes of the first Avengers film. The scene hinted that he is the overlord of villainy, the Big Bad who the Avengers will face in an epic battle in a future film. We also realised then it was Thanos who sent Loki to get the Tesseract from Earth, while giving his own sceptre. In the first Guardians of the Galaxy film, we get to see a bit more of Thanos, though he was still sitting in the sidelines. The movie also informed us that he was after the Infinity Stones. Avengers: Endgame: Fan Theories Predict Captain America Will Wield Thor’s Old Hammer Mjolnir in the Final Battle Against Thanos.
So after watching Thanos find all the Infinity Stones and decimate half the living universe in a matter of a few hours in Avengers: Infinity War, some of us had to ask this - why the hurry, purple Bruce Willis? Didn't you wait for 18 movies for things to heat up? Good question, and there is an equally good answer, or rather interconnected answers for that.
So before we get to watch Avengers: EndGame on April 26, let us clear this one niggle some Marvel fans have about Avengers: Infinity War.
#1 Thanos Didn't Know Where All Stones Were Exactly
Thanos began his journey with one stone in his possession - The Mind Stone - which he lost thanks to Loki. So he was back to nil by the time the first Avengers movie ended. Thanos didn't know really where the rest of the stones are, unless they are being used. Like SHIELD's work on Tesseract made him realise Space Stone was on Earth. Jane Foster discovering Aether in Thor: The Dark World could have notified Thanos about Reality Stone's presence. And likewise, for Power Stone in GOTG and Time Stone in Doctor Strange. It was easier for him to get to the Stones, once they were discovered. So by the time Infinity War arrived, Thanos only needed one stone's location to be discovered - Soul Stone - which Gamora gave it to him under pressure (and loses her life in the process).
Don't go by our word. The recent clip from Avengers: EndGame confirms that use of the Stones can be tracked even if it is happening on another planet.
#2 The Space Stone Helped a Lot
Travelling through limitless Space is not an easy task; just ask Tony Stark and Nebula who are stranded on a spaceship when Avengers: EndGame begins. While MCU still makes it look easy, we expect travelling from one galaxy to another to take at least days or even months in their unbelievably fast spaceships. Which is why the Russo Brothers made Space Stone the first Stone that Thanos retrieves in Infinity War (though he has already got Power Stone from Xandar, which was said not shown to us). With the help of Space Stone, Thanos could travel anywhere in Space in a matter of minutes, working the same way as Bifrost. This made his 'hurry' to get the rest of the Stones easier.
#3 He Waited For the Most Powerful Warrior to Die
Captain Marvel may be the powerful superhero in MCU; Thor may be the most powerful God that is alive. And yet, Thanos wasn't really scared of them. But there was someone who was so powerful that Thanos had to operate in the shadows to get the stones. As per a popular fan theory, Thanos was waiting for the All-Father, Odin, who is Thor's dad, to pass away before he comes out in the open. Which is why Thanos never dared to get into Asgard despite knowing that the Tesseract would be there. This could also be the reason why he sent Loki to attack Earth, thinking that Odin won't tackle his son directly. With Odin 'dying' in Thor: Ragnarok, it was one big hurdle away for Thanos in his mission to get the Stones. And Ragnarok almost confirms this by bringing Thanos' ship in the mid-credit scene of the film.
It is the combination of these factors that explains why Thanos was in a tearing hurry to get to the Stones. Who knows, these points may also come in play during the events of Avengers: EndGame too. So watch out!