If FSI would pay line captain rates they'd have instructors that would never leave (and be experienced in type). That's always been the issue - the gap between line pay and instructing. The $$$ tends to go up when the industry is hiring. The demo is also changing a little. FSI used to be considered a retirement job (collect your military pension or airline pension and sit back and have health insurance and make some money). Now there's a lot of people in the 35-45 range.
For those that came from a bankrupt airline or furlough years ago and have accrued raises, seniority, months of sick time, etc. It's tough to go back to that gig again because you've got to factor risk in the equation. I believe that's a prevalent mentality. As Climb450 said, there's a bigger payoff in the long run on the line; however do you give up what you've got and take the risk. As they say, the house always wins....