Shake shack is so much better then in and out... Bbops is king though and really miss that now that I am out of Iowa.
After having been in CA for a while I'm pretty sure the reason In and Out is popular with locals is that it's by far the cheapest place to eat including fast food like McDs. People with a family can take them to Shake Shack or 5 Guys once or In and Out twice for the same price.
Tourists on vacation go because they've heard about it and feel they must try it (I did). They are often let down because it's just a simple burger and small menu...but for locals I think it's just everything costs so much and it's a very good value. Their milk shakes are actually pretty bad, the fries are unique but cut fresh. The burger is good but like you said Shake Shack is objectively better.
Is In and Out life changing the way some people act? No. Is it way better quality than McDonalds and somehow costs less? Yes.


