1. Evolution does not work the way too many modern people think it does. It’s not about purposes and intentional changes. It’s about creatures tending to be the same generation after generation, except for some random mutations, and then when and IF some massive threat wipes out most or all members who have or don’t have certain traits, THEN the population has more survivors with those traits.
2. Have you ever lost a thumbnail? I have. They serve at least two purposes. First, they protect your toe a bit from some bumps that toes do tend to get, which the soft top of a toe otherwise will suffer more from. Second, it feels to me like it improves the structure of the toe for grip/traction purposes. It feels better. Without a nail, that toe felt both more vulnerable, and weaker.
They’re annoying to clip, though.