I feel the problem with In-N-Out is that people get disappointed because they expect too much. Their competition is not Shake Shack, or Five Guys, or some one level below restaurant quality burger place. They are meant to be an alternative to Burger King, Wendy's and McDonald's. That's where the hype comes from really, that for the same amount someone can drop at those places, In-N-Out is a vastly superior product.
I'm from the East coast and didn't have it until I was like 23. I lived in MD since I moved to the states so I had eaten a lot of Five Guys. If I had to pick between the two it is a toss up. But Five Guys cost much more.
I like In-N-Out for what it is. When I was dead broke in college getting my Masters,it was probably the best meal I would have for the week. Now I have it every once in a while. I mainly go when I take my girl's lil cousins after a soccer practice. The food is good, the place is always clean, the service is outstanding. The bang for the buck is great, and that's really how they stay so popular with locals. For their price point, it is have to beat for what you get.
And the menu is dead simple. It is really like three main options. And you don't need to know any secret menu lingo. Ask the personal taking your order, and they will quickly run down popular off menu items people get. It ain't that serious.
Finally the fries are kinda meh, but the issue is that they can't change them because too many people will complain. And it would cause a massive hassle.