Let's start with the loyalists:
Lion El'Johnson: long, flowing, kept blonde hair.
Jaghatai Khan: long top knot.
Leman Russ long flowing, sometimes plaited hair.
Rogan Dorn: short white hair, untameable.
Sanguinius: long, flowing hair.
Ferrus Manus: short, closely cropped dark hair.
Roboute Guilliman: short, closely cropped hair.
Vulkan: shaved / bald scalp.
Corvus Corax: long, flowing hair.
summary: 5 long, 3 short, 1 shaved/bald.
And now the nominal traitors:
Fulgrim: long, flowing, kept white hair.
Perturabo: bald (or at least unknown under all that cerebral piping).
Konrad Curze: long, lank and probably unwashed dark hair.
Angron: bald/shaved with lots of pipes coming out of the scalp.
Magnus the Red: long flowing hair.
Horus Lupercal: shaved / bald scalp.
Lorgar Aurelian: shaved / bald scalp.
Alpharius: shaved scalp.
summary: 3 long, 0 short, 6 shaved/bald.
Yes, that's right. The traitors lost because not a single one of them had short closely cropped hair. If only Horus and Lorgar grew theirs slightly longer like Ferrus and Dorn, the tide might have turned… but all that head shaving lost them the war. Or perhaps Curze just needed to be introduced to shampoo. We're not sure.