-to signal virtue for PR purposes -to expand hiring pools and thus drive down wages -to get more sexual partners -to create leverage points for internal politics (e.g. opportunities to accuse political opponents of sexism)
Perhaps you were actually asking about bad outcomes, not reasons:
-women are rationally perceived as less competent after they were given preference during hiring -women who would have been happier in another field are encouraged into tech where they are less happy than they would have been in medicine, or law, or marketing, or at home -women who aren't up to the task are admitted; the mismatch sets them up for failure where they could have succeeded and had better personal outcomes in another job
Both my above lists are offhand samples.
diversity is generally considered a good thing in evolution. i dont know if that applies to concepts like the tech industry, but maybe it does.
i am not against anyone and think the universe of software is a big one with a ton of room.
software is not created in a vacuum, nor is any other art or form. i want us all doing it, not just a bunch of people like me in every way.