Why are boys more dominant in baldness than females?

The term dominant is a misnomer here as the trait is not dominant or the number of women with the trait would be much higher. Pattern baldness is a sex-linked trait.

Male pattern baldness alleles are present on the X chromosome which means that only one copy of the allele is required for a male to exhibit the trait (the y chromosome, being much smaller, doesn't have the gene locus for this trait).

Females must have 2 alleles for the characteristic in order to exhibit the the trait.