I'll quote an excerpt from Lea Verou's exquisite article on sexism (http://pensieve.verou.me/post/47360690848/what-is-sexism) that I think helps answer this in a broader sense:

There is a lot of talk about what’s innate and what’s acquired. Characteristics we considered male or female for centuries are constantly being proven a result of nurture, either completely or by a large part, as tiny innate differences that grow intro troublesome gaps with social conditioning. Modern neuroscience keeps demonstrating how adaptable our brains are, and how society takes on the role of conditioning them on fixed gender roles from an incredibly young age. Have you ever noticed how gendered toys or child TV programmes are? How many people keep telling little girls they’re pretty and little boys that they’re smart or brave? That’s only the start of a rabbit hole that goes quite deep…

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So much of it is Western culture. Here's one great example of another culture where women are not so much "welcomed" as they are just people - http://www.hanselman.com/blog/HanselminutesPodcast203WomenIn...