A lot of times people yearn for promotion only because their peers are promoted. At least that's what I saw in Uber. When Uber had only a handful of senior/staff engineers, few people were vocal about promotion. But when Uber suddenly promoted a large number of people, everyone was screaming for a promotion. In contrast, few engineers in Netflix complained about titles for all ICs had the same title - this may be selection bias, though.
That is to be expected, similar to the way open discussion of salaries puts upwards pressure on salaries. When Bob sees Alice get promoted, he asks himself why. Maybe it's obvious that Alice is a better employee, but not by so much that Bob feels it's out of his reach. So he works harder and then asks his boss if now wouldn't be a good time for that promotion for him too.
Or maybe it's not obvious why Alice got promoted and Bob didn't, so Bob asks his manager. Hopefully the manager can explain the reasoning in a way that Bob can understand, and Bob can get to work to level-up or can accept that he's just not as good as Alice. (If the manager can't come up with a good reason...well...that's a problem. For the manager.)
If no one's getting promoted, then there's not much point in asking for a promotion. May as well keep your eye on jobs at other companies if you'd like to get ahead. Sometimes companies try to keep the promotions quiet, in an apparent effort to suppress the masses clamoring for a promotion. I suppose it works, as much as suppressing salary discussion works. ("Here's your annual raise this year, you did a _great_ job, this 3% shows that, almost _no one_ gets 3%, this is super high. Great job, Bob! Oh, and don't worry about that promotion, it's super rare to get promoted within your first x years at the company, it'll come...")
