Symphony orchestras used to claim to be the equivalent of a 'meritocracy' (don't think that they used that term, though). They selected strictly by audition, relying on the ears of the (male) conductor/director, and less than 10% of the musicians selected were women. When they changed to have the musicians perform behind a screen, and without identifying them by name, the number of women selected increased dramatically.

A similar dynamic happens in the tech world. The people determining 'merit' have that same built-in bias against females, and will judge their work as lower than it should be. The bias need not be conscious, and in most cases the men think that they are being fair and honest, but it's there.