http://steamcharts.com/app/440
There's a number of issues biggest one is our playerbase in general has been horribly stagnant. We're at our lowest point since May 2014 for average players. Even then it's not really a big decrease we've been around 45k-55k for the most part since 2012.
Only Valve can fix that. Getting rid of a lot of cheaters last month will likely see some people come back to the game. Whenever valve does their performance patch then we'll likely see a ton of players comeback.
As for competitive there's a lot of things that can fix that, most of which rely on Valve. But all things considered TF2 has a much healthier competitive community than any other FPS outside of CSGO. Every CoD league since MW as soon as the developer stops pumping money into the game which is usually less than 6 months maybe 1 yr dies and dies fast. Battlefield 4 at it's largest was fractional in size to their equivalent tf2 league on that continent. So all and all tf2 really isn't doing that bad.