This really is a be careful what you wish for moment. Truth of the matter is that the Cubs are way more talented than the Marlins. They've got guys like Bellinger that have a great track record in the playoffs. You really don't want to tempt fate and try to lose on purpose just to play these guys again next week. Yeah the Marlins are playing better, but the playoffs are a different animal.
And not to mention if they just give them these 3 games, the Cubs gain some confidence and think they can beat the Brewers. Like I said, they're a talented team, probably just as talented as this Milwaukee team if you look at run differential. Just because they're down now doesn't mean that's what'll happen next week.