Earlier this morning I was watching Angel and it dawned on me, they changed sets for their final season. Angel went from a hotel to the Wolferman & Hart LA headquarters for their sets. BTW, this was before my learning they used virtual / green screen sets in Sanctuary. So, I guess the new sets wouldn't be a reason to cancel Sanctuary.
Here is another thought and one on why it will return: The series is NOW in a position to do a complete reboot of what the series represents and the characters. It can address issues presented by focus groups, etc. Well, just a thought . . .