why do you think Dream told Sam 'all about exile'? obviously, this didn't lead to pleasant consequences for him
it's interesting, right? especially because--while exile wasn't exactly the most unknown thing at that time--it's far from the highlight of c!dream's Villain Actions in the majority of the dsmp population's collective consciousness, at this point. it's been about a month since c!tommy ran away from exile, and since then c!Dream has done Doomsday and then the staged finale. for someone like c!sam, it makes a lot more sense for c!dream to judge him as caring more about how Fran would've been taken as leverage in the disc vault, or how their old home together the community house was blown up by dream. while i have no doubts that c!sam would've interrogated c!dream about exile anyway, c!dream didn't have to tell him "all about it" in a way that had c!sam completely horrified within that first week. and frankly, no matter what cruelty c!sam might've already been up to, c!dream wasn't going to crack to the point of confessing anything he didn't want to confess over the course of like, five days in the very beginning of the prison arc.
so why does he? i'm sure he'd give you a whole host of rational reasons. c!tommy can't keep his mouth shut, obviously, so he assumed that c!tommy would spill the beans sooner or later. provoking c!sam from the getgo gives him a good idea of what to expect from the rest of his stay here, which will help him navigate the situation in an optimal way. mentioning c!tommy affects c!sam obviously, emotionally, which keeps him too off-balance to think about any logical inconsistencies in things like the staged finale and ever suspecting that c!dream wanted to be in the prison in the first place. if he's forthcoming about this Terrible Crime, then c!sam will be too focused on interrogating him about tommy to ask questions about the revive book, or vikkstar and lazar, or punz. and so on.
they're good enough reasons. valid reasons, sure. c!dream is very good at coming up with lists of rational reasons behind his actions, objective courses of actions that leave him firmly in control. c!dream also--in the process of the plan to put himself in the prison--dies at least five times, as far as we know of, and likely many more (if we are to believe that he did experiments on his own limbo pre-prison, which i think we Should, considering the circumstances, then he needed to lose his initial three lives to even test the revive book on him, not to mention however it was that he got another three lives in order to lose two in the staged finale) and starts swimming in the lava not even 24 hours into his imprisonment. just because a reason makes the most sense or is the most rational doesn't make it the real reason why c!dream does much of anything, which is something he never quite gets around to admitting to himself.
like i know i talk about the c!wilbur of it all when it comes to discduo like a lot but. listen. exile might’ve been the point of no return for them that sort of made friendship no longer an option, but the exact moment they become enemies isn’t exile or the disc war or spirit speech or the duel. it’s quite fucking literally the exact moment tommy raises that crossbow at wilbur and dream steps between them.
“wilbur, hand me that tnt” “tommy, I’ll— I’ll have to step in” is the exact moment that takes discduo and defines their entire fucking story. that exact moment is why boundless sands has to exist for the discduo finale to even happen.