It's as simple as the rules say what the roles of the DM and player are, and the players describe what their characters are doing, not the DM, short of exceptions like magical compulsion or the like. It's not really any sort of grandiose principle. One of the roles of DM is to mediate between the players and the rules, so the DM is well within their role to tell them no-go on having gloves here. I personally would not much care about something so mundane, so fine, they can have the gloves - record them on your character sheet please - and I'll introduce another complication that reasonably follows from their stated action.
Now, the rules also serve the DM, not the other way around, so you can decide not to do any of this and take control of the character as much as you like. But as has been shown countless times, this just invites more conflict when the DM describes the character as doing something the player doesn't agree with. That is so easily avoided that I wonder why anyone continues to do this at all.