There are a number of reasons why homemade croutons might not turn out crispy. If you bake them at too high of a temperature, they will brown before fully drying out which leads to soggy croutons. Too much oil can also cause them to be soggy. If your croutons aren't fully cool and dry when you store them, moisture from the inside of the croutons will cause all of the croutons in the container to become soggy.