Why are lethal dominant alleles so much more rare than lethal recessive alleles?

Lethal alleles cause the death of an organism prenatal or after the birth. Lethal alleles are usually a consequence of a mutation and they can be recessive, dominant or conditional. Since the lethal dominant alleles are harmful whether they are carried in homozygous (e.g.AA) or heterozygous (e.g.Aa) form,  a strong selection against them is present and thus these alleles are much more rare.

digestion

it excretes wastes