Why do work places jerk you around for a promotion? They promise and promise and say how great you are but it never comes

I was supposed to be made into a shift lead because I bust my ass and everyone knows it and I know what I'm doing but I keep getting jerked around and it's been months now. I asked long before those months even started. Everyone whenever I confront them about it just smiles at me and I get no answers. If you don't want to promote me don't instill false hope into me and I swear the only reason I've stayed was because of that hope of a promotion. Now that it's obvious that;s not happening I'm going to start filling out apps for new jobs. I'm not wasting my time anymore. Go ahead and hire all your friends like you always do because when I'm gone and I will be you will be sorry you didn't promote me and you will be sorry you jerked me around all this time.

I'm taking people with me I got several people all fired up and ready to walk because they like me get treated like second class citizens in favor of the bro squad