Question

why do frog produce a large number of gamets

Answer 1

as frog reproduces in water many of its eggs is eaten up ..by aquatic fauna and many get destroyed by natural causes only some will survive...so for continuation of their species they reproduce so many eggs....

Answer 2

Amphibians like frogs reproduce by external fertilization. That is, the female and male gametes fuse outside the frog's body. This usually happens in water, thus there is a possibility that the male gametes never make it to the eggs, unless there are lots of them.