How does resonance make some carbenes less reactive?

The reactivity of carbenes is reduced through the phenomenon of resonance, which provides internal stabilization to the molecule.1

Resonance occurs when multiple electronic structures, or resonance forms, can be written for a single molecular type. The actual state of the molecule is considered a hybrid that incorporates characteristics of all these forms, making it more stable—and thus less reactive—than any individual resonance form would be on its own.1

In carbenes such as difluorocarbene and methoxycarbene, substituents like halogens or oxygen atoms allow for the creation of these resonance forms. These structures involve shifts of electrons that produce positive and negative charges, effectively stabilizing the divalent carbon atom. By contrast, highly reactive carbenes like methylene lack such stabilizing substituents, leaving them without this internal electronic support and making them significantly more prone to chemical attack.1