Because if you raise the price of your pickup $20,000 and Toyota doesn't then you're discouraging customers who see two similar vehicles with a significant diff

Because if you raise the price of your pickup $20,000 and Toyota doesn't then you're discouraging customers who see two similar vehicles with a significant difference in advertised price. And if you try to work with the other companies to move prices up together, that's illegal. Same for airline tickets.