Gas stations change their prices based on their primary supplier for a given area these prices tend to be more or less the same, they also don’t make money on selling gas these days but rather of the convenience store/restaurant or by leasing that space to someone.
It's true that they don't change prices daily, but it's also not particularly uncommon for them to do so. Visa raised an assessment I think last January? And interchange fees have changed several times over the years as well.