If I had to guess, I would say the largest deciding factor for Babcock in Spezza over Shore would be their role on the penalty kill. Spezza's played 2:49 on the PK and was on the ice for 2 goals against. Shore has played 4:54 and hasn't been scored on yet.
The
first goal against was the Atkinson one against Columbus. Face-off to the right of Andersen where Spezza wins the draw after a bit of a scramble but he puts it past Muzzin. Andersen tries to play it... misplays it... and then a Columbus players gets on the loose puck and fires it into the net.
The
second goal was a one-timer by Stamkos. Spezza was playing the box near Stamkos' side and didn't collapse to him. If everyone who ever left Stamkos open for a PP one-timer got scratched though we'd be running out of NHLers.
With all that said though, why does Spezza even need to play on the penalty kill to be in the line-up? I don't get that. Both him and Shore are already behind Mikheyev, Marner, Kapanen, and Moore as those guys are the core 4. They're also slightly behind Gauthier, who plays the same FOGO role they do. And soon enough they'll be behind Hyman when he returns. That's 6 guys who can play on the PK ahead of either of them. Is Shore more useful to the team in a very, very limited PK role than Spezza would be playing consistent PP2 minutes?