Because making broad assumptions about 50% of the population isn't a cool thing to do. Especially given the excessive amount of nonsense women in tech (and not in tech) have to deal with on a daily basis. Talk like this leads to women feeling excluded from the tech community.
Also, specifically calling out "young women" as not being interested in tech really makes a lot of assumptions. Generally, people will talk about most topics - even if they aren't passionate about those topics themselves. Most women I know will happily talk about tech stuff with me, so maybe your approach is wrong.