Captain America couldn’t hold Mjolnir before the Endgame because he kept Bucky’s secret. Here’s why the other Avengers aren’t worth it.
Fans began to understand what Mjolnir deserved Thor when Odin cast a double spell on it with the following inscription: “Whosoever holds this hammer if he be worthy, shall possess the power of Thor.”
The other original Avengers were not worthy because they were never unselfish, never sacrificed for the greater good or the bravery that never manifested.
He remains an Iron Man to deal with his fraudulent weapons business. He creates Ultron, so the Avengers are no longer needed. Ultron destroys Sokovia, endangering the Avengers. He never really got redemption.
When he first refuses to contact Thanos’ cancellation of Snap, even after starting the family, Tony can’t leave it, and Pepper recognizes it.
Natasha puts it best in Age of Ultron, which is how Bruce always runs from the fight, and the others run towards it. He never wants to be a hero, and he always joins in the fight when he has no other choice. In Thor: Ragnarok, he became The Hulk again to save the Asgardians, even though he knew he might not be Bruce again because he didn’t see it any other way.
She doesn’t give up after Snap, trying to help the Avengers as a hero, but there’s always unfinished business. She acts unselfishly, but she is never really selfless. She is haunted by her past, and sacrificing herself is partly to save Hawkeye and his family, but ultimately to redeem it.
Hawkeye keeps trying to retire for a good reason. He has a wife and children, but when he needs to be a hero, he returns. However, when his family disappears after Snap, he goes on a killing spree.
The original Avengers were all heroic, but they never deserved Mjolnir. The key to worthiness is total selflessness and complete absolution. Some may disagree and believe Captain America was always worthy of it; he is still one of the original Avengers along with Thor, who deserves Mjolnir.