Update: I just took down the motor clutch. No obvious problem as long as I could tell. Nothing appeared worn out. I cleaned and lubricated the clutch and put everything back, but the problem is still the same. I realized the clutch really can spin without the outer drum, which connects to the belt. Even when I rotated the center part together with the clutch in my palm after taking it down from the motor, the drum didn't have to rotate together. Why is it designed like that? Now I understand why the center axis spins without the drum/belt. Because they are designed to be separate. I am not a mechanic after all. Why it's designed that way? Just tested the washer again and it spun for a few seconds then stopped. Tried again and it would not spin anymore. I even tried to move the basket in spin mode manually while holding down the lid switch. The belt below could move, but as soon as I stopped spin it manually, it stopped. I am really out of clue. Very frustrated.