Bloomberg writes that "grocery sales accelerated in late May and early June," confounding analysts " who expected robust grocery-store sales to diminish as the year progressed and as vaccinated Americans returned to offices, restaurants and travel. It can’t be explained by inflation, because grocers are also returning to their normal practice of discounting, which partially offsets the price hikes they’re taking elsewhere. Sales of groceries on a unit level, which exclude the effects of inflation, have held steady."
Two reasons are cited in the Bloomberg piece.
First, "online ordering has made it easier for shoppers to buy more, with curbside pickup and home delivery removing the hassle of lugging items through the store and checkout."
And second, consumers have "a greater sense of preparedness instilled by last year’s lockdowns, when many essential items were hard to find." Shoppers don't want to be caught unawares again.
You can read the entire analysis here.