It didn't fit

The Gauntlet altered its size to fit the Hulk's hand. It's possible that it was designed to resize itself for whomever tried to wear it, but it's more likely that Tony was directing the shift using his mental control over his nano-machine suits. If that's the case, then there's no way for anyone who isn't Hulk sized to put the gauntlet on until Tony can get there to resize it.

It's also possible that the power surge from the Stones shorted out the Gauntlet's reshaping capabilities. We never see it do anything other than mechanical movement until after Tony comes into contact with it at the very end (and even then it's not clear whether he was interfacing with it directly or using parts of his current suit to steal from the Gauntlet).

It didn't occur to them

It's very easy to get tunnel vision during high stress situations. Nobody who had their hands on the gauntlet had much time to think critically - they were too busy fighting for their lives. Once it was established that it was vital to return the Stones to their own times, it simply didn't occur to them that the Stones could be used for a different purpose.

They didn't know that they could

Thanos snapped his fingers and killed half the universe. Does that mean that you can snap your fingers and kill a specific group of people? Is there like a dial you have to turn from the "kill half of everything" setting to the "kill the bad guys, but nobody else" setting? Tony has a much better idea about how to control the Gauntlet and use it for his own purposes than most of the heroes who were trying to transport it.

Also, Spider-Man at least (and probably a few of the others) didn't have the stomach to murder an entire army with a finger-snap, even if it would save lives. This isn't universal though, so it doesn't get a header.

Because that was never the plan

The plan was actually to get the Gauntlet and the Infinity Stones to the quantum tunnel in the van and use that to put the Stones back into their respective timelines. The plan only changed for the Tony snap when Thanos destroyed the van and Tony had to improvise.

HAWKEYE: Cap, what do you want me to do with this damn thing?

CAPTAIN AMERICA: Get those stones as far away as possible!

HULK: No! We need to get them back where they came from.

IRON MAN: No way to get them back. Thanos destroyed the quantum tunnel.

ANT-MAN: Hold on! That wasn't our only time machine. Anyone see an ugly brown van up there?

VALKYRIE: Yes! But you're not gonna like where it's parked.

IRON MAN: Scott, how long you need to get that thing working?

ANT-MAN: Maybe ten minutes.

IRON MAN: Get it started. We'll get the stones to you.

_{Avengers: Endgame}

Let's see who all had the gauntlet:

• Hawkeye: He had personally seen what the Gauntlet did to Hulk. He was definitely not going to survive using the Gauntlet, and he knew it.




• T'Challa: He had barely seen the Gauntlet just once. He had no clue as to what it was.




• Spider-Man: He was a kid, just back from the dead, and teleported to that location. He was in no condition to make the decision.




• Marvel: While she could have wielded it, she too had no clue what it was. From her perspective it was merely a Gauntlet to be returned to the van.

What Tony did in the end, was out of desperation. They were losing. Unable to contain Thanos and his forces. He saw Thor and Cap try and fail. He saw Marvel try and fail.

He knew he had to do something big. That desperation, combined with the fact that he designed the Gauntlet at least in part gave him the confidence to at least try using it.

Extended speculation: Outside of all this, I think the Iron Gauntlet was completely fried from its first use, and lost its ability to shrink back to normal size. No human-sized hand could have fit in it, much less be able to use it.

Any one of them could have used the Gauntlet to end the battle much as Tony did.

Actually, no... As I wrote in my answer to Why didn't other heroes use the Gauntlet while they were playing catch with it? on Movies.SE, there's an interview confirming that basically, only Hulk (and Tony) could do it. You have to remember that the Gauntlet is equipped with all six Stones at that point, which is a whole lot to handle. Even Captain Marvel might not have been able too, and she's easily in the top 3 of overpowered people in the MCU.

Sure, that interview only talks about the "final" snap, but it's probably valid for partial actions as well - in the heat of the battlefield, you won't stop to take a Stone off (to "ease" the manipulation for instance), fire part of a power, reslot the Stone... Sounds like a nice way to lose one, which would jeopardize the overall plan of "in the end, use all six and unsnap".

Q: Why Iron Man has to be the one to do the final snap, couldn’t the people like Thor, Star-Lord or Captain Marvel whom all previously have handled the power of Infinity Stones done it instead?

A: Thor in this movie couldn’t do it, only Hulk was strong enough to do the snap without dying. We are still not sure whether Captain Marvel can also withstand all the power of Infinity Stones at once. The reason we choose to let Iron Man do it in the end was because he was the closest one to Thanos at the time. In all the futures Doctor Strange foresee, Iron Man was the only one who could get close to Thanos and do the snap.

'Avengers: Endgame’ directors just explained some of the movie’s biggest mysteries, BGR, April 30th, 2019