Everyone who plays TF2 has been playing forever.
The game has arguably the worst new player experience out of all video games ever created, no real community to speak of, gigantic unfixed glaring issues, and is basically dead. There's no fucking chance that new players are suddenly going to flock to TF2, leaving only the "old players" as the community.
How does the new player experience compare to Valve's other flagship game, DOTA 2? The skill floor in that game is a lot higher.