Workplace conspiracies

 Everyone with a job knows how its feels to be passed up on a promotion you know you deserve. In addition, everyone around you gets the promotion you worked hard for and you wonder "what the hell". Even though the people that get raises and promotion really and truly didn't earn it. We all hate it and it makes us wonder "when will I get mine".
I've been employed at my place of employment for three years (long time, right). I've been getting passed up on getting a promotion for a while not but recently, the company I work for changed their policies.   I don't know how they are doing it but it's weird and confusing. People I know for a fact don't work as hard as I do or even have seniority for that matter (the company mostly promotes people that have been there a little while). It's annoying because last year and most of this year I work my ass off trying to make management. To be honest most of the people in management slack off a majority of the time and really don't put in work. This is irritating because now, everyone is getting recognized for their mediocre work and I barely get a good job.
I know most people, really great workers have this problem but what does that say about management? Is management so blind they can't recognize leaders? I'm totally not dissing management but I'm asking what's going on? I know it's a fact of life that most people don't get what's rightfully theirs but when do you draw the line?