Again, the cartel(s) existed (and they've long been accused of price fixing of various kinds; BigAg price fixing fines are not new; https://en.wikipedia.org/wiki/Lysine_price-fixing_conspiracy as an example). The handy "it's the pandemic's fault prices are going up everywhere" excuse to get away with big price hikes was new.
They didn't need excuses to raise prices, this explanation still doesn't explain why they waited. Cartel's don't care what their consumers think since they've cornered the market on an inelastic product.