why does natural selection make organisms have traits that are helpful but not necessary for the species’s survival?

Question

For example our hands become wrinkly after getting wet so our ancestors could grip onto trees better after swimming.

Would we really go extinct as a species if we didn’t develop that extremely specific trait at one point?

Same for crying as an emotional response, or eyebrows keeping sweat out of our eyes, or goosebumps making our hair stand to be more intimidating to predators.

I understand why these would be helpful, but I don’t see why these were so necessary to the human race’s continuation that nearly every human has these traits.

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Answer 1

Evolutionary pressure can work even under very subtle evolutionary pressures. If a simple change means a population with an adaptation is 1% more likely to survive, over generations that builds, 1% improvement in fitness still means after 100 generations there will be 2.7 times more individuals with that adaptation than not. Over 500 generations, 144x more individuals.

This is just the power of exponential growth.