I am going to make an educated guess, based on my knowledge of evolutionary theory. As you know, we share a common ancestor with other primates, for example, the chimpanzee and the gorilla. In fact, our DNA and the DNA of the chimpanzee are remarkably similar. What do you think about when you think about chimpanzees and other primates? You probably picture them climbing and swinging through trees. Imagine how helpful their toes are. Even though we don't do this too much, our toes still help us to navigate when we are climbing up or going downhill. What do you do when you are trying not to slide on a slippery surface? You curl your toes to have a better grip. If the bottom of your foot had no separate, flexible digits at the end, you couldn't do this at all. So toes are still useful to us, and as long as they are, they will enable us to survive and have children to pass those toes on to. Of course, this is an oversimplification of evolutionary theory, and I hope you are interested enough to learn more. It explains so much about us!
Good luck to you.