Except they really don't, because each aisle of your grocery store only has two actual companies making 90% of the products, and coke does not compete with pepsi on price
If Pepsi doubles in price but coke does not, you will not see most pepsi drinkers switch to coke, you will see a small amount of pepsi drinkers abstain, a small amount of pepsi drinkers switch to coke, and the majority of pepsi drinkers just grumbling about paying more.
We've had decades of shrinkflation at this point. I can't use a recipe from twenty years ago because it calls for 15.5oz cans when we've already moved to 14.7oz cans of that product. I can't buy a competitor's version because they use the same can and same can sizes.
A great demonstration of this is something I've been bitching about since "inflation" happened. Lays (the same company that owns pepsi) massively increased chip prices. So did their competitors. Our regional store brand DID NOT (because potato prices did not increase for over a year!). Our regional store brand is comparable to basic chips from other brands. Predictably, people just paid the higher price for lays and the competitors who also raised their prices.
The past several decades, companies realized that consumers have WAY MORE stickiness to a "brand" than ever realized. People still buy craftsman tools, including my father the contractor, despite them being cheap garbage for decades now. Companies don't compete on prices because there is only one competitor in each market segment, and they love the sky high profit margins too. It's not worth it to gain an extra 5% of the market by lowering your price significantly, which is what it would take to get the extra market share. Consumers aren't rational, they are tribal. Nobody drinks pepsi or coke, or prefers red vines to twizzlers, because of some rational evaluation of product merits.
What DID switch people from pepsi to coke was not price, but marketing!
