Stock cams and stock valve springs don't put as much of a load on the cam bearings, so the stock bearings are adequate for that application. If you put in a performance cam with more lift, you increase spring pressure so the stress on the cam bearing increases, and of course with a performance cam, you will tend to drive it harder.
With a series of JIMS tools Rogue replaced INA cam bearings with the tougher Torrington jobs.