Why are difluorocarbene and methoxycarbene less reactive than methylene?

Difluorocarbene and methoxycarbene are significantly less reactive than methylene because they benefit from internal stabilization provided by resonance.1

In these molecules, the presence of substituents with lone pairs—such as the fluorine atoms in difluorocarbene or the oxygen atom in methoxycarbene—allows for the formation of resonance structures that delocalize electron density. This phenomenon creates alternate electronic structures that contribute to the overall stability of the molecule, making it less prone to the highly reactive behavior characteristic of methylene. While methylene is one of the most reactive molecules known, the resonance forms of difluorocarbene and methoxycarbene effectively lower their energy content, thereby reducing their chemical reactivity.1