It's magical sexism. Everyone agrees in the abstract that sexism must exist, but there are no actual incidents that can be positively attributed to sexism.
Sexism is like racism. It's a pattern of behavior. It is difficult to determine that a single act is motivated by sexism unless the actor uses terminology that deliberately casts it in that light.
That's the way this stuff works, and why it's so hard to fight. Racism, sexism, homophobia, the list goes on. The reason is that bigotry isn't conscious, it's subconscious.