The proof is in the pudding: There are less women in STEM fields and in STEM programs in college. Even making the grandiose assumption that women have the exact same opportunities as men (see above, they don't) fewer women are accepted to universities, they matriculate less, and even less stay in the field. Males on the other hand seem to do just fine. This reveals to us that there is a disparity at each step of the way that is causing women to be unable to compete or desire to.
When one person drops out, it isn't a trend. But when you have industries full of this data combined with a history of sexism and racism, you don't throw your hands up in the air and say "oh the boat will right itself".