Why wont the bigger 2-3lbs trout bite at my bait?

The bigger trout 2-3 lbs i believe, at the lake i fish at will not bite at anything. Im having no problem catching the younger and smaller trout along with blue gill and crappie. I have been using 6lbs test original stern line, so i don't believe the line im using is too big. As far as bait it has been small, kastmaster lures, fake minnows, and worms. All have worked well with the smaller fish, but the bigger trout wont bite at all. I see them swimming the lake shore all the time, but they are not interested in my bait. The lake is Trinity Lake in Northern CA.