Beaudin is a former first round pick of the Blackhawks in 2018, but is now struggling to make the lineup of a desolate Blackhawks team. After bouncing between the NHL and the AHL the last few years, and struggling to put up many points, it looks like Beaudin will only amount to an option for a depth defenceman.
Hillis, from the Canadiens, is a former third round pick of the club, a center prospect who has also bounced between the Canadiens and their minor league team. Also putting up underwhelming numbers in his NHL and AHL stints, like Beaudin he appear to be an option for organizational depth.
Perhaps both clubs would prefer that organizational depth in the separate positions, and that's what motivated the trade. It could also be a trade of two failed prospects both looking for a reset with a new team. Most likely however, it's an extremely inconsequential trade to both teams.