The objective being that they could sit back and bluff Roglič until he feels he has to work to defend his lead from Quintana, with the aim that Roglič would then get tired working alone against the four Movistar riders up front plus the stagehunting Deceuninck riders, and then once he is tired, THEN Astana kick into full gear, fresh and with probably a good 20-25km left to mitigate losses, plus potentially gaining time on a Roglič that would have had to spend 15km in the wind. You know, remember the 2010 Giro and how it ended up with Vino and Scarponi and Evans taking pulls in the remainder of the péloton while Porte and Arroyo still had domestiques up front? The bonus is that Pogačar was also isolated so they could have potentially had the same fortune against him. We saw today that yesterday's exertions cost Quintana, who had been looking weak in the mountains at the weekend. Surely they'd fancy their chances of taking 3 minutes from Quintana more than their chances of taking the same amount of time from Roglič on the evidence of the last two weeks?
I have yet to see a single justification on why would Roglic work alone against the Movistar riders upfront and not simply let the Rabbo/Bora/UAE doms work for him that isn't some implicit "lol i dunno i'm just a bit of a kook who fancies making up completely absurd scenarios".