I understand why they do it to some extent.
If the Atalanta coach didn't think there usual tactics were going to get them anywhere, it's only right to try something different.
His little adjustment towards 3-5-2 was fair enough. With Schelotto and Peluso, they have the players to make that adjustment.
It is of course possible that they hadn't really planned to play an open game, but Juve scoring early caused them to change.
I doubt the change would have been so immediate, though, so I imagine they planned to have a go at Juve.
Their defence should have been deeper, their midfield should have been closer to the defence and either Moralez or Bonaventura needed to try and close Pirlo down.
As it was, there was nothing to stop Juve moving the ball around a a high tempo and find space in different areas of the pitch.
Having a go away to a good side is fine, but you need to at least keep things compact early on and give yourself a platform in the match before trying to open up and take the game to the opposition.