They're in bodies they don't know, on a world they don't know, fighting for one bunch of total strangers against another bunch of total strangers over causes they've probably never even heard of and certainly don't understand. The climate is different, the language and culture is different, the wildlife and vegetation is different, the atmosphere is different. Shit, even the gravity is different. They know nothing, and even if you download them with implanted local knowledge, it's a massive amount of information to assimilate at a time when they're likely to be fighting for their lives within hours of sleeving.