That’s because In N Out doesn’t spray their fries with sugar water. That’s what every other fast food joint does, so you’re just not used to the taste. Ask them to double dip the fries if you want them crispier, but the “bland” flavor is your sugar addiction talking.
I don’t believe that’s it - it’s not any underlying sweetness I’m missing. Rather, it’s texture and flavors - or lack of them. As bad as their burgers are, Five Guys makes terrific fries - their Cajun fries are outstanding. Thick cut, perfect texture when served hot, just the right amount of seasoning. If In-N-Out could just figure out how to make fries like that, they’d be the perfect fast food place. Everything else In-N-Out makes is outstanding.