They do all the standard retail stuff to keep people in the store longer (most common staples at the very back, etc.), but they also regularly move stuff around to make things harder to find, and rotate a bunch of seasonal merchandise in and out all the time so there's always new stuff to look at in the store.

A long answer to say, 2 hours probably isn't uncommon for Costco shoppers. I don't think I've ever spent 2 hours there, but I'll bet lots of people do.