As a manager you may have 10 people reporting to you. Some do more important work, some do less important work, but when you are considering them for promotions there are other factors too. I am not talking about promotions from junior dev to regular or regular to senior, I am talking about promotions to positions where they are responsible for other people. In my almost 30 years working in IT in multiple companies I found that most good technical people are not good managers; similarly most managers are technically bad. Best managers are the ones that Steve Jobs described in one of his famous interviews (I will leave the pleasure of having him tell it, it is worth spending the 3 minutes).

In any case, there may be others doing more important work and there may be others better suited for promotions. It is a zero sum game, the number of people, positions and promotions is always limited so if X is promoted, Y cannot be and if X is a better one for the promotion, Y will have to either wait, move on or keep doing what they do.