[member="Joran Greth"]
A fair point. The only Admiral I can think of that did that was Thrawn.
General it is then. Thank you!
[member="Galven Solomon"]
The reason is because an Admiral is usually in charge of a fleet, or a Captain of a ship, as Stormtroopers are not part of the army, but their own organization, and not necessarily have an equal rank officer. For example a Captain (at least in US Navy) is the equivalent of Colonel in the Army.
For Star Wars where the ships and formations are larger, it would make sense that a Captain would technically rank "higher" or as high as a general or like army officer. And thus would be the officer in overall command of all forces. I don't know if this is actually the case, this is just my guess.