Probably a combination of both just women's personalities and gender discrimination.
Men may just be more flamboyant or showy when it comes to displaying their talents than women are, so they're more likely to be noticed and become 'famous'. And a lot of becoming executive chef is in who you know as well.
For discrimination... it's probably not direct discrimination, and the people that do it, are probably not doing it intentionally. For instance, when people view a man and woman doing equally well in a job, they're more liklely to feel the man achieving well because of natural talent or ability.... but for the woman, they're more likely to view that she's achieving well because she's a hard worker. Now, both of these have the same results (cooking well in this case)... but if one is doing well because they're working hard... then if they're not working hard, they'll fail... or their 'limit' of achieving would be finite. So somebody who is doing well because of natural talent or ability is seen as better and prefered.
And what makes this even more profound, is that the more attractive the man, the more likely people are to view the man's achievement as natural ability... and the more attractive the woman, the more that her achievements are based on her looks or hardwork, and NOT talent. And in becoming famous (as well as most things in life), being attractive is a definite plus.
This is just the tip of the ice berg when it comes to discrimination and stereotypes.