Because (and, again, not an economist, so I apologize if this is full of teh dumb) people selling things want to make as much profit as they can. So they’re going to raise the prices as long as someone is willing to pay them.
Bring the numbers down for a minute so we can play with them more easily. Say Bob’s Widgets sells 100 Widgets a month at $100 each. He has a sale, maybe he sells 110 Widgets at $90, his daughter needs braces, so he raises prices for a month and sells 90 Widgets at $110 - but basically, no matter what he does with a modest shift in the price, he’s averaging around 100 Widgets a month. Widgets are a “luxury item”, you see. Everyone wants a Widget, but it’s not a necessity, so poorer folks go without and wish they had a Widget, or they buy a Widget on credit that they can’t really afford.
So then Governor Smith decides that everyone should be able to afford a Widget if they want one. He sends everyone a check for $100, so they can get a Widget. Suddenly, Bob can’t keep Widgets in stock! He sells 100 Widgets in a week and they’re beating down his door for Widgets! This is great, right? Bob gets sales he never dreamed of, and even poor people get Widgets!
Then Bob realizes he can’t keep up. He hires Mike to come work at the Widget store with him, and raises the price of Widgets $5 to cover Mike’s salary. Then the two realize they need more space to accommodate all these customers, so they rent a new store and raise the price of Widgets another $5 to cover the rent. The sales of Widgets slows a bit, because now they’re $110. But they’re still selling pretty briskly - maybe they move the production offshore to reduce the cost back to $100.
But pretty soon, Bob thinks, “Hmm…I used to sell 100 Widgets a month. Now I’m selling 100 Widgets a week. I bet I could raise the price on Widgets and people would still buy them.” So now he sets the price of Widgets at $150, then $160, then $175. And pretty soon, either people are so addicted to the idea that they’re entitled to a Widget that they dip into their savings or credit to come up with the difference, OR they can’t afford a Widget again, because Bob has raised the price. But because he’s making essentially the same amount of money off fewer people, there’s no incentive for him to lower the prices again.
Indeed, many items *suffer * sales if they become too popular - make Widgets something that poor people have, and rich people won’t want it. Bob would rather keep the rich - people who might buy more than one Widget, or upgrade their Widget every year or so, or buy accessories for their Widget - and lose the poor who can only buy their one Widget with their check from Governor Smith. So Bob may even intentionally raise the price to the point where he loses some sales so that Widgets remain a product that not everyone can afford.
In fairly short order, we’re right back to where we started: the rich people buy Widgets and the poor people wish they could or go into debt to get them. It’s as if no one got a check in the first place.
Now, what I don’t know is if this pattern applies to actual necessities. I don’t know if the price of eggs follows this pattern.