The Marvel Universe uses a lot of MacGuffins
A MacGuffin is a plot device everyone is after, and there’s plenty of those in the Marvel Cinematic Universe. Half the movies Marvel has done are based around MacGuffins, especially the whole first cinematic arc, which featured a stupid nondescript object called The Tesseract, which is never really explained in any of the movies. It is apparently an object of great power and has other-dimensional origins or powers or something, which Thanos knows about, for some reason. How? Why? Who knows. Who cares. MacGuffins don’t answer questions, so stop asking. They’re there to move the plot, like these:
The Infinity Stones = This is what moves the plot of Guardians of the Galaxy. The characters don’t know where the stones came from or what exactly they do. They know they’re valuable and powerful, that’s about it.
The Tesseract = Marvel likes this MacGuffin so much they used it for two movies. It barely moves Captain America: The First Avenger at a good pace, but does a better job in The Avengers, where people can’t stop talking about it.
The Aether in Thor: The Dark World = The main villain has a mega-weapon, which is a MacGuffin. Thor wants to stop him (and it) and the villain wants to unleash it. Thor does a horrible job of that for a while, until he finally stops Malekith in an overdramatic climac. There’s no mention of what happened to the MacGuffin after Malekith dies, but apparently it is gone.
The Hulk in The Incredible Hulk – The second Hulk movie doesn’t technically have a MacGuffin because the Hulk himself is the most classic MacGuffin in the whole Marvel Universe. He’s been chased more times than Speedy Gonzales. Everyone wants a piece of the Hulk for some reason, and NOBODY can leave the Hulk alone in this movie.
The Winter Soldier = The evolution of MacGuffins in the Marvel movies ends with this one because this one doesn’t use one either, but it is similar to The Incredible Hulk for using a human MacGuffin. The Winter Soldier is the MacGuffin this time around, and everybody wants to know who he is.