In the MCU, it's established that you need to be a very powerful being to wield the Infinity Gems.
If you remember in Guardians of the Galaxy, all of them had to hold hands to try and harness the energy of the Power Stone. If it was just Quill, he'd have died. That applies to Jane in Thor too, the Aether was killing her.
In Endgame, for a short moment even Thanos, the mighty, holds the powerstone to fight Captain Marvel, but he too had to return it to the Gauntlet.
In fact the Gauntlet has been crafted specifically to host the stones without killing the person wearing it.
The Snap is all the stones being harnessed at once. When Thanos does the Snap in Infinity War it really destroys his one arm and leaves him terribly weak.
When Hulk, who is also pretty strong, Snaps, his arm needs to be put in a sling.
Tony, in spite of his suit, is nowhere as powerful as the other beings who have wielded the stones directly or through the gauntlet. Performing a Snap is far more than he can take. And hence dies from it.
In short, performing a Snap is not like wishing for something from a Genie, you need to be physically powerful enough to endure the action of the Snap.