Possible explanation: In the US, who started tech field expansion earlier than other nations (70's) the first wave of IT managers got their original IT training in the military. They tended to run their IT departments a bit like they did in the military so it was a very masculine culture. This started to change when that wave of managers took retirement in the late 90's, but by then IT in the US was estabished as a "guy thing."

Obviously there's more to it than that, but that pops into my mind.