Plus Arabs are pussies.
Eh, I think a lot of Israelis who fought in 1973 might disagree with you.
They're not hopeless or genetically incapable of being good troops. The British-trained Jordanians were quite good. On a tactical level the Egyptians between 1968 and 1973 really got themselves respectable though they still ended up screwing up on a grand-tactical and operational level once they got over the canal.
And historically the Arabs managed to beat the Mongols (something they share in common with the Vietnamese; few countries were able to beat them) so they've had their moments in the past.
Their military problems since WWII are largely a result of corrupt government and the problems resulting from that.