Haemophilia is rare in women because
Women are homozygous
Haemophilia is a sex-linked recessive trait. The trait is associated with the X chromosomes.
Women are homozygous so they have XX chromosomes as sex chromosomes. They will exhibit the disease condition only if they are homozygous recessive i.e both the copies of the gene are defective. With just one defective copy (recessive allele), it gets masked by the good copy(dominant allele) and the women become carriers.
Males only have one X chromosome, they have no spare normal chromosome to override the chromosome which is defective.