This is because genetic hemophilia is an X-linked recessive disease, like colorblindness. That means that while a woman has two X chromosomes, a man has only one X chromosome (and on Y chromosome). If a woman is carrying the disease on one of her X chromosomes, she still has one 'clean' chromosome, and will not show hemophilia. If she has two 'infected' X chromosomes then yes, she will show it, but that means that basically her father has to be a hemophiliac while her mother is a carrier. If a man's mother (or father) is a carrier, then they can inherit an X chromosome that does have the gene for hemophilia and will have it, because that means that all 1 of his X chromosomes are 'infected'
