Why must reptiles and birds use internal fertilization?

Reptiles were the first fully terrestrial vertebrates to
evolve on Earth. One adaptation that allowed them to live a terrestrial life was the
evolution of the amniotic egg and internal fertilization. With internal fertilization,
there is a greater chance of the sperm to be delivered to the egg and for fertilization
to occur. This is in contrast with Amphibians, which have external fertilization in a
freshwater environment. There is a risk that many of the eggs will never be fertilized
by sperm and thus, thousands are released to help insure some become fertilized.
However, after the female reptile or bird lays the fertilized eggs, they are equipped
with various membranes to support the embryo. These include the outer porous shell
and the chorion which is a moist respiratory membrane beneath the shell for gas
exchange. There is  the allantois, to store wastes, the yolk sac to provide food and an
amnion for the embryo to develop in. All of these adaptations made reptiles and later
on, the birds able to successfully reproduce on land.