I've not been doing it long and was guilty of thinking the same thing, what's the point in fishing a stocked stillwater. The fact is there's a lot to learn just like sea fishing. I thought it was just a case of turning up and filling your boots but that's definately not the case. I like fishing dry flies and flies that sit in the surface film. The amount fish that swirl at a fly and sink it is frustrating but exciting. There's a definate knack to fishing buzzers properly that I haven't quite mastered.
Think of it this way, you head up northumberland to fish for summer cod, you know the fish you are targeting, you kind of know there should be some lurking about. You fish with a mate who is having a good day and your pretty much emulating him and blanking, it's a similar thing really. As already said, catching on a stocked water, trout anyway, is not a dead cert mate.