So, there's the answer.
The Imperial Army does/did exist, but is/was phased out in favor of Stormtroopers.
And that covers a lot of ground.
See an Army trooper? He's with a unit that hasn't been phased out yet.
Why have them when Stormtroopers seem to do the same job? The Empire agrees, it's just a slow process.
Need them for your campaign? It's canon.
Don't want them in your campaign? Also technically canon.
Those guys Driving the AT-ST? Imperial Army. The infantry was phased out, not other units.
Edited by Ghostofman