This is from The Kitchn (2011), but is probably still accurate regarding the expense of pine nuts:
"So why are they so darn expensive? There are a few reasons. First there the obvious climate changes that are affecting crops worldwide. More specifically, most of our pine nuts are grown in China and Russia and in the past few years the crops have suffered in quality. All the while, demand is growing as more and more people are becoming acquainted with recipes for pesto, sauces, and savory desserts.
Also, pine nuts are labor intensive. Remember, they’re really just edible seeds produced by pine cones. Plain and simple. To gather those seeds from the cones takes time. Combine poor crops, a labor intensive product, and a greater demand and you’ve got your answer."