Actually QF had the 146 on a number of these routes for years, but as with all boardroom decisions the economics of the Q400 came out miles ahead and made any future replacement look EXTREMELY expensive.
The Q400 would be operating on routes where the 737 wasn't economical and DJ were only running the trunk routes.
For
VB to gain some ground on routes they haven't touched till now, they needed something that was more
PR than anything else to try and lure the frequent flyers.
Once you have them onboard, you have their business over the entire network!