Supervised fault classification requires labelled failures, and the whole point of a well-maintained plant is that failures are rare. A plant with three bearing failures in five years cannot train a supervised classifier on bearing failure.
So the practical framing is anomaly detection against a healthy baseline, combined with the physics: bearing defect frequencies are calculable from geometry and shaft speed, so a rising component at the ball-pass frequency of the outer race is interpretable without ever having seen that failure on that machine.
Physics gives interpretability. Learned models give sensitivity to patterns the physics does not enumerate. Used together they produce alerts a maintenance engineer will actually believe — which is the binding constraint on the whole application.