Why is there so much ism by bouncers in Melbourne's nightclubs?

Often I hear stories of how clubbers in Melbourne are denied entry because they happen to be male or because there's not enough females in their group. Being private establishments, they can make their own conditions for entry but don't you think it's ridiculous how people are denied entry based on gender? Also, why is that people need to be in groups, often 3 or more people to be granted entry? Shouldn't clubbing also be about meeting new people rather than just socializing with your immediate group whilst you're there?