Maybe - just maybe - there is a commercial reason for them to take A320s? I mean, the chief of Network also introduced them to Skywest when they were servicing the same major client. And maybe, just maybe, it will only be a couple of old, cheap frames that Network operates, mostly on charter. After all, in NW conditions the A320 outperforms the 738.
The big advantage of the A320 in WA is the fact that they have lower pressure tyre options than the 738. Some of these mine strips are quite low strength pavement.