Why is it always biceps curls?

I'm sure everyone has already seen the pictures of Paul Ryan at the weight bench.

But this isn't really about Paul Ryan. It's about biceps curls, probably the most useless weight exercise going for a regular person who wants to build muscle and stay in shape. I call them "the Doritos of fitness".

For some reason, someone curling a dumbbell has become shorthand for "weightlifting", and thus for "fitness". I guess it's partly the different angles you can photograph someone from. Squats can be kin...