The demand fell, supply went up dramatically and there's a new equilibrium.
Very few advertisers are actually in a true "prisoner's dilemma" in the sense that they're fighting tooth and nail in the same market as another company and parsing back advertising will cost them dramatic marketshare. First, a lot of demand is supply constrained - lysol is going to sell their wipes no matter what, so advertisers can easily defect. Secondly, advertisers may be locked in a competition broadly but not in a specific channel. Your youtube channel probably isn't your best ROI or its easy to cut back spend and just invest in your most performant channel - it's often not youtube for these companies.
Very few advertisers are actually in a true "prisoner's dilemma" in the sense that they're fighting tooth and nail in the same market as another company and parsing back advertising will cost them dramatic marketshare. First, a lot of demand is supply constrained - lysol is going to sell their wipes no matter what, so advertisers can easily defect. Secondly, advertisers may be locked in a competition broadly but not in a specific channel. Your youtube channel probably isn't your best ROI or its easy to cut back spend and just invest in your most performant channel - it's often not youtube for these companies.