The van der Waals ferroelectric NbOI₂ hosts a polar distortion that is commonly attributed to the Peierls dimerization of its Nb chains. Here we show, using first-principles calculations and a Landau-type energy, that the polar instability is in fact a distinct order parameter that does not stem from the Peierls mode condensation and that three main distinct modes are important in the whole MOI₂ family. They are a polar mode P, an antipolar mode η, and a Peierls mode δ, whose stabilities and couplings strongly depend on the nature of the M metal element, as evidenced by the fact that the isostructural, TaOI₂ system is not polar while possessing Peirls distortions.