Probably because you would need to harvest immense amounts for them to work as a staple food source, and their pretty bland flavor, at least of the various sort

Probably because you would need to harvest immense amounts for them to work as a staple food source, and their pretty bland flavor, at least of the various sorts I've tried, is not really something likely to make them a luxury food source, though I'd have said the same thing about caviar. With modern farming technology the mass cultivation may be possible, but for times past compare this to something like a single decent sized whitetail deer that can provide upwards of 100 pounds of edible meat. One deer = months of food. One insect = minutes/seconds of food.