You haven't been exposed to a very broad range of parents. I've seen parents who very tightly control which toys, clothes, and grooming choices their kids make because they don't align with the parent's gender expectations. It's frustratingly common in the US.
And yeah, I think it's a potential contributing factor (one of many). Kids in many parts of the country are socialized that certain things are only for certain genders. It sucks. Let kids like whatever they want.