Starfleet may not be the US military, but it is a military in function and form, so to have officers who stay in the same grade and position for a long period of time really doesn't help anyone but themselves. That is the wrong type of attitude when you are in uniform. Besides all that experience and knowledge that La Forge has accumulated should not be wasted on a select few serving in the engineering section of one starship, he should be using that wealth to help his fellow engineering officers grow and make starships even more efficient and and safer.