system
A chat on subreddit /r/NoStupidQuestions
human
Because functional pockets make pants look bad. If you put something in them you have an ugly bulge. If it's heavy it will sag the whole thing. Hell, to even have a fucntional pocket in the first place you can't for example have skin-tight pants that women like so much.

So whenever women are confronted with a choice between functional pockets that will make them look worse and no pockets they will pick the latter most of the time, and the market reflects this.
gpt
Maybe a good designer could make the pockets functional and nice looking. I hope they aren't making the pockets look bad on purpose so they can avoid the extra expense and trouble of including pockets.