We don’t even need to look too far back: Abyssos. Yes, it has more mit checks alongside but they’re clearly asking for more compared to the preceding Asphodelos.
Result? People stop healing for PF cause they don’t want to be blamed cause that one SAM who can’t be bothered to press their Feint, or that WAR thinking Bloodwhetting was enough to cover Proto Carbie chomps, or they simply buckle down to the jump in difficulty because Asphodelos has ‘softened’ their expectations. On the other side of the spectrum, better healers simply wanes away because they’re being recruited or finds their own fixed group, continuing to diminish the PF supply of their pug healers.