High-pressure superconductivity in metal monochalcogenides has been ascribed to disorder-driven Anderson localization [Phys. Rev. Lett. 134, 196001 (2025)]. Using density-functional perturbation theory and Migdal-Eliashberg calculations, we show that superconductivity in BiSe, PbSe, PbS, and HgS is instead governed by a universal intrinsic mechanism. Under pressure, the superconducting transition temperature is fully regulated by conventional electron-phonon coupling and decreases monotonically with pressure due to phonon hardening and a reduced density of states at the Fermi level. The increase of $T_c$ previously reported upon decompression arises from the recovery of stronger intrinsic coupling in metastable low-pressure phases, without invoking disorder or localization effects previously used to explain this phenomenon. Our results establish a unified phonon-mediated description of superconductivity in metal monochalcogenides and solve conflicting interpretations.

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• Electron-phonon coupling
• High-pressure studies
• Chalcogenides
• Elemental superconductors
• Density functional perturbation theory
• Eliashberg theory
• First-principles calculations