Would my salary be higher if I become more productive? No. My salary is fixed. I get my bonus even with a minimal effort.
Will I work less if I become more productive? No. I still have to spend 8 hours par day at work.
Will I get more work to do if I become more productive? Yes. As soon as I report something as finished, I get more work. And expectations grow.
Being more productive doesn't benefit me, my coworkers, even my company or the society as a whole. It only leads to more stress and strain.
Then why would I want to be more productive? I'm fine spending my 35-40 hours "working" and making "work" for me and my coworkers as comfortable as possible.
And when I go home, I'm not tired, but refreshed and ready to go on with my life.
EDIT: I'm saying this as actually one of the top performers at my company. It's politics and bullshitting that gets you more money and promotions, not hard work. But that's the game I refuse to play. Instead, I focus on doing the least amount of work I can get away with. Say "Wally" from Dilbert, but without being an asshole.