Answers (2)
Some don't hatch, some don't get fertilized, some get eaten before they turn into frogs, some die before they turn into frogs (I'm sure that there are other ways for them to die), the eggs could've been eaten, water level goes down and dries out all the eggs, etc, etc, etc
*just a few that I know
It's all to do with God's plan.There is on our planet what is known as a natural cull. It applies to every creature including humans(unfortunately).The frogs that remain follow the natural order of their existence.For your information there are about a hundred speices of frogs, and believe me there are thousands.I don't know how you came up with the figure one hundred. Our frogs lay up to a thousand or more eggs.