"Achieve mastery through challenge" is the tagline. The idea here is to push yourself to solve problems you may have not attempted before, and to learn from others by seeing how they solved theirs. I've have personally learned a lot from seeing how other people solve problems, I even learned a lot from creative uses of solving "Hello World" which was a bit of a surprise.

In short: Codecademy is meant for those who want to learn programming. Codewars is for existing programmers who want to get better at programming.