http://i.gyazo.com/0d315cc0773a65b480dbefed9031157f.png
You are talking about CONCURRENT players, which is the number of people that are playing the same at the same time. As the picture shows, it peaked at 450k today, and it is 270k at the moment. My picture shows the number of unique players (i.e. different accounts) per month. Over 5 million. The CS:GO player base is huge, over 5 mill..
Also, the reason that you might not hit a 1 hit hs is that because even when standing perfectly still , bullets don't go straight. There is a small box where the bullets hit. Obviously the further away the less accurate you are. Apart from that, you have to account for lag and all those shenanigans.