I cannot help but imagine that our Lower 48 trout are so wary, that they prefer itty bitty bugs most often (in most places) because they've had the snot pounded out of them so hard by way of people pressure. Pressured trout are binge feeders (not opportunistic predators), and it takes an epic event (e.g. a salmonfly hatch) to trigger the binge. Other than that, they feed to subsist, and that's why you have to spoon feed size #20 black beauties to the trout in Cheesman Canyon (CO), for example. Remove the pressure, and trout lose inhibition. That's why 18-inch cutthroats eat Humpies and Royal Wulffs in the backcountry.