What is the significance of the toad statues in Mount Myouboku?

Question

In Chapter 409, it's said that they were people who failed Sage Mode training and were turned into toads and eventually into stone. But there don't seem to be many people that signed the summoning contract, so they can't all be from people who failed Sage Mode training.

Why are there so many toad statues? So where did they all come from?

Answer 1

According to here:

There is a sacred fountain on Mount Myōboku which produces a special oil which allows people to more easily feel the natural energy around them, but if the person is not perfectly still, becoming one with nature, he or she starts becoming a toad and eventually turns into stone. This oil can only exist in the atmosphere of the mountain, and will evaporate if taken outside. There are many statues of the frog ancestors and of people who tried to learn senjutsu, but failed and became toad statues. The statues are treated with much respect.

People live at Mount Myōboku, and some can use senjutsu, so it stands to reason that there would have been a number who failed.

To address the other part of your question, Minato (the Fourth Hokage) is also known to have been able to summon toads, which shows that it isn't just Naruto and Jiraiya who can summon them.

Answer 2

There are many statues of the frog ancestors and of people who tried to learn senjutsu, but failed and became toad statues

Copied from here, so statues are not just of people but also frogs.

When you say,

But there doesn't seem to be many people that signed the summoning contract...

That's not true. In the anime/manga they have shown only Naruto and Jiraiya's story. But it is assumed that like Naruto and Jiraiya there might be many other people from other centuries that tried it.

Answer 3

When you see the toad contract in chapter 92 page 18 you don't see the full scroll. You only see six signatures. There are most likely more people who signed farther into the scroll and then failed the sage training.