Why do frogs not lay eggs in salt water?

Frogs are freshwater animals. The saltwater would kill the eggs and, if they survived, it would kill the tadpoles, dehydrating them.

Also, not all species of frogs lay their eggs in water, e.g. the Corroboree frog does not.

Also, frogs of the genus Pristimantis lay their eggs on land, where they do not undergo a tadpole stage, hatching as fully metamorphosed baby frogs. Some species of frogs even give birth to live young, such as members of the African genus Nectophrynoides and other species found in the Andes and Central America.