it is quite common in big organization
It tells me that your department may not have big influence in the org. so that even though you are the best employee in this department, they can't push a promotion through when balancing the budget with other departments. What this is saying is that if you want more career development for yourself, it is time for you to move to a more business-critical department. Your boss and your boss' boss apparently are very good. So it is your decision what is more important.