Why are there two Infinity Gauntlets?

It makes sense to have two gauntlets, one for each hand. But it doesn’t make any sense in the MCU, especially since there are only enough Infinity Stones to equip one of them. Obviously, one of them is fake – but which one? We guess we’ll find that out in the Infinity War…
However, the question still remains. One was in Odin’s vault, while one is with Thanos. Are we to expect that any of these two powerful characters can be fooled so easily? Are we to expect that either Thanos or Odin doesn’t have the necessary resources to find out that he doesn’t own the real one?
And this raises yet another question: Isn’t this bad writing? Isn’t this an easy way of resolving probably the biggest question of the entire MCU? With the Gauntlet and the Infinity Stones, Thanos is basically undefeatable. Having a second (and real) Gauntlet would solve so many problems for the heroes, wouldn’t it?
