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human
[Star Wars] Why do we almost never see Imperial Army Troopers if they outnumber and are deployed more than Stormtroopers?

According to the Star Wars lore in both Canon and Legends Imperial Stormtroopers are supposed to be a smaller military branch of elite troops and the Imperial Army Troopers vastly outnumber them and make up the majority of the Empire's ground forces. If this is the case then why do we almost never see Imperial Army Troopers? Even the backwater Imperial warlord states in The Mandalorian use Stormtroopers.The only time that we see this dynamic between the Imperial Army and Stormtrooper Corps is in Solo a Star Wars Story. Also if Stormtroopers were supposed to be more elite than Army Troopers then why is it that in the show The Mandalorian former Imperial Army Trooper Mayfield mocks the Stormtroopers ability?
gpt
The army digs in and slogs it out. Stormtroopers go where the action is the heaviest and act as an all around defense/offense force of the navy. We rarely visit worlds that survived for long against the empire in open warfare or were actively fighting. We do see naval leaders chasing the rebellion and New Republic through unsettled and uncontrolled systems. 

The reason we see the army so rarely is because they're a completely different breed from the stormies. Army forces rarely left their bases unless out fighting. They rarely fought strategic battles and moved like an army hitting an entire planet or ground force not a strike team. The army had no way to travel themselves and relied on the Navy to ferry them around. The Navy relied on stormtroopers and regularly used stormies for expeditionary forces or more traditional ground combat forces until the army could arrive. The two branches filled overlapping but distinct roles seperated mostly by their personal dedication to the empire and their association with the navy.

Post endor the reason you only see stormtroopers is because mudtroopers and other army types were typically conscripts forced into service not loyal citizens. Remove the threat of imperial retribution and pensions and only those loyal or fully indoctrinated would remain in service.