The problem isn’t lost weapons.
The problem isn’t the weapon being taken from the good guy.
The problem is stolen weapons. A gun stolen in 1940 is still good to go today.
Maybe the Mafia types really do drop the weapon at the site (at least they do if they pay attention to the movies), but the guy sticking up the Rob-Me-Quick doesn’t - that old revolver is his meal ticket for the rest of his career.
Is this meant as a joke? Preventing such situations is one of the precise goals of such a device. I don’t know why you’re assuming that it’d always be a Good Guy taking the weapon from the Bad Guy, or why the Good Guy would then care that the weapon is no longer usable. If I somehow got myself into a situation where I wrested a weapon away from an evildoer, I would first try to render the weapon incapable of firing, and then would throw it as far away from both of us as I could.