I don't think that the US minds losing a few Predators.Those are designed to be expendible.It's the same everywhere-for eg India,Israel,Pakistan have all lost drones in enemy territories,but it's rarely been humiliating for them.
Expendable yes, but it would be a major propaganda coup for the North Koreans to exhibit the wreckage. In this time of heightened tensions this would simply be giving the N.Koreans an easy target to down. Exactly what they want to show the world that they are simply defending themselves from the US.
The North Koreans have been blowing hot air about the periphery recce flights for some time now. They showed their frustration by mounting an intercept of an RC-135 last year by their MiG-29s and MiG-23s. The RC-135 crew felt threatened and exited the area.
There is simply no need antagonise the North Koreans further by conducting direct overflights. Furthermore UAVs, U-2s, RQ-4s are vulnerable over such heavily defended airspace. The US are not going to risk recce configured F-14, F/A-18s in this manner either. North Korea is left to airbreather stand-off sensors and satellites.