3. Actually, Thanos DIDN'T Have A Gauntlet In 2015
The Infinity Gauntlet has caused Marvel Studios some serious headaches over the years after that Easter Egg appearance back in the first Thor. It's almost like they should have just NOT put it in there, no matter how hard they've tried to explain it away as a clever inclusion since then.
But that's not the only Gauntlet appearance that makes no sense and that was quickly retconned, because it happened again in the wake of the supposedly "real" Gauntlet's appearance at the end of Age Of Ultron. In that film's post-credits scene, Thanos retrieves the Gauntlet from his own vault to start collecting the Stones. It's seen as him kicking off the real Infinity Stones Saga.
Except, it's then dropped out of logic again in Infinity War, because Peter Dinklage's Eitri reveals that Thanos forced him to create the Gauntlet specifically as a vessel for the Stones' power. It wasn't an existing artefact and it was created AFTER the events of Age Of Ultron, according to how Eitri describes Thanos' attack on Nidavellir.
The creation of the Gauntlet there makes the idea of a fake Gauntlet existing even more problematic. Even though Kevin Feige said the fake was put in Odin's vault to reassure the Asgardians that the All Father had control over everything that would be a threat to them, how the hell did he manage to create a fake that looked identical to something that would only be made as a one-off years later?!