I worked as an Engineer as well as a Project Manager in my past (for the electric company in Tampa). There, and at other places I worked there are two basic types of bosses.
First those the see your suceess as their success and subsequently promote you. They look good because you make them look good so they want to share you.
Secondly, those that hoard their own success achieved on your efforts and subsequently want to keep you all to themselves. They too look good because you make them look good, but they are selfish. They want to keep you right where you are for fear once you leave you'll leave them in the dust and they then need to succeed on their own merit.
The latter is more prevalent than the former.
Be the good boss, promote your stars.