I know, its fucking stupid right?
Yes, the original imperial army was made up of clones but they took years to grow and be ready for the initial takeover of the weak and fractured senate but many regular folk later enlisted to stop the terrorist threat that the rebels represent.
The whole point of Palpatine taking over was to create Order, sure, a few races were marginalised along the way but prosperity and opportunity were increased for the vast majority and joining the Imperial Navy means a steady paycheck, the chance to work with state of the art equipment and travelling the galaxy has its perks too.