Our primate ancestors required tails so they could effectively move around on trees. A tree dweller without a functional tail is slower and has a harder time gathering food and escaping from predators. That's a very strong selection pressure that ends up maintaining the tail.

When the woods in eastern Africa changed into savannah, we shifted to two legs and adopted a persistence hunting strategy. The tail became useless, even a liability, and mutations that resulted in reduced tails were not selected against anymore.

Natural selection doesn't require 100% disqualifying, it just needs a slight preference and a shit load of time.

>Plenty of people wear artificial tails today and get laid

…Do they? What did I miss?