In a previous study, it was proposed that a real graviton acquires an effective mass of order the Planck mass $m_P$ owing to nonperturbative quantum gravitational effects at distances of order the Planck length $l_P$, leading real gravitons to form an aggregated film structure. Physical arguments in that study further suggested that this graviton film surrounds every proton. Here we show that such a graviton film substantially suppresses proton decay within the framework of grand unified theories (GUTs), rendering proton decay effectively unobservable experimentally. This mechanism accounts for the non-observation of proton decay to date and reopens the viability of GUT models previously considered excluded, including minimal SU(5).