For SW3, the left root path has a cost of 2,000,000, and the right path has a cost of 2,000,000 + 200,000 = 2,200,000. It chooses the lower cost = left path.
If the link between SW2 and SW3 was 100BASE-TX as well, the cost would decrease to 400,000 and SW3 would choose the right-hand path.