One Theory Is That This Concept Was Invented by Parents

I've never really understood the idea that a "beach read" should be something light and fluffy. On the beach, you can relax, you have the time to get into anything. I could see wanting something light on the subway--you have to be able to get into it right away and follow it amid all the jostles. I guess the point is that when you're at the beach, you're far from the library. So what you really want for the beach is not necessarily something relaxing or easy to read, but rather a sure thing, a known quantity that you'll definitely enjoy.

Andrew Gelman, "Beach Reads, Proust, and Income Tax"