Just a reminder of the obvious but easily forgotten:
There are many other
possible reasons for this besides merit or lack of confidence in Martinez. Martinez might have requested it this way.
First of all, other than 9 years at Georgia, his pattern has been 4 years or less with any one school or head coach. Despite the squawk from some fans, that pattern has not been for lack of
success developing players or improving pass defenses. So there's something there to the way he (and his family) rolls. I think it's safe to figure he enjoys the challenge, as long as he can work with excellent athletes.
He has three children, so at his age it's likely he and his wife are or will soon be grandparents. Others here can attest to how that changes a person's goals in life--but especially when one's career has put his family through so many location changes. He and his wife could be looking to relocate closer to grandkids, or relocate closer to aging parents, or even retire from football to enter a second career in something other than coaching.
There's even the possibility that Martinez forewent the raise this year, to free up money for Heupel to keep some promising young coaching talent in-the-fold. We've seen how Heupel prefers to promote from within when he encounters a coaching vacancy.
As I said, I'm only offering this as a reminder. We really don't know, and sometimes we jump on these theories like a coonhound on an unfamiliar scent trail.