Not to rebut your point, but how many people play BF4? It might just be that TF is a bad game to some degree.
Not as many as you'd think. There are plenty of people that just can't be bothered to buy it on Origin or dislike EA/Origin enough that they skip the game. Steam has a very, very large userbase. If you saw a Steam friend playing Battlefield 4, you might be more inclined to purchase it.
As it is now, you've got to fire up the bullshit Battlelog (terrible idea) thing and hope it accurately shows who is online.
I don't know anyone that thinks highly enough of Origin to make it their default platform. EA fans have sort of just begrudgingly put up with it. Free games are cool too, I guess. It's just not added value, which is the entire point of Steam. Piracy becomes more likely and problematic when you've got twelve different clients and storefronts.