When they measured their performance against his, many were equal or even stronger than he was in their sales numbers. His only advantage was that he had been with the company longer. In the minds of his peers, that was not a valid reason to give him a higher title. To pacify a couple of strong sales managers, and to try and put the issue to rest, the company promoted two more managers to director level. It may have made the grumbling lessen, but it didn't solve the problem.
Some companies have a rigid schedule for promoting staff.
You start at the entry level with the company and in three years you move from account representative to account manager. Three years later, you're senior account manager, then director, then vice president and so on. Typically, everyone moves along that schedule. Some companies use schedules to ensure that the people who have worked there the longest have the biggest titles. These companies are missing the point that promotions come as a result of performance, not as a reward for sticking around a long time.