According to one source, the reason for the sudden storyline change in attitude and confidence in Big Show this week on RAW is likely because of Vince McMahon's rumored return to television, which is expected in the near future.
The storyline surrounding Big Show lately has seen him say "how high" when Triple H and/or Stephanie McMahon say "jump," until he was fed up with their abuse and defied their orders with his actions in the main event at WWE Battleground on Sunday. This led to his overly confident attitude when being dressed down by Stephanie McMahon in the opening segment of RAW on Monday.
Apparently the reason for that is Vince McMahon, who is scheduled to return to television earlier than originally planned due to recent extreme dips in television ratings and other business projections, will come back as a babyface that will defend Big Show. This would allow Big Show to be confident, as we saw on Monday, despite the fact that his superiors, Triple H and Stephanie McMahon, are threatening his job.