it does.
if you win as white
0.5 x 0.3 = 0.15 (win win)
0.5 x 0.2 = 0.10 (win draw)
0.5 x 0.5 = 0.25 (win loss)
0.25+0.1+0.15=0.5
draw as white
0.2 x 0.3 = 0.06 (draw win)
0.2 x 0.2 = 0.04 (draw draw)
0.2 x 0.5 = 0.10 (draw loss)
0.06+0.04+0.1=0.2
loss as white
0.3 x 0.3 = 0.09 (loss win)...