Because they're all making record profits by all raising prices. Why stop the gravy train?
So, what is on one hand necessary and inelastic can also be a luxury.
Even things called 'staples' are flexible, you won't die of malnutrition if you don't eat eggs.
Which is exactly my point: either a rival corporation would be able to get market share via undercutting, or price increases are not actually that sensitive to consumer to begin with.