Because, human beings never counted claps before medium introduced this “button”.
Surendra Vikram Singh

Hm, I can see the reasoning behind their decision though. From what I understand, it’s was more about Medium Partnership Program where they tried to come up with the system that would compensate writers fairly. Not all stories are created equal and while you may enjoy one story, you might appreciate another a lot more. The scale give members the tool by which they can reward some stories more than others because writers get paid more for stories that receive more claps. I wonder whether all Medium Members are aware of that…

One clap, two clap, three clap, forty?

By clapping more or less, you can signal to us which stories really stand out.