Trent Green said that "it was hard to overcome the comfort factor" as part of the pull that led him to sign on as the Rams backup QB.
An $8.9 million contract can make a backup QB pretty comfortable too.
It does seem pricey for a backup; he'll make $4 million this year. Not all of that will count toward the cap since some it comes in the form of roster and signing bonuses.
For Al Saunders there's certainly a comfort factor as well. The Rams get a backup who should have to spend the bulk of the summer learning the offense. He already knows it. There's definitely some value in that.
There's also a message, albeit a subtle one, to Bulger, reminding him that Green can just as easily run this offense. There were rumblings under the surface that Bulger didn't exactly go all out last season. Now whether or not that had to do with Linehan's futile attempt at running the offense or knowing that the o-line couldn't protect him is debatable. But from the coaches' POV, this ensures there's nothing short of 110% bleeding out of the pores of the guy they made one of the highest paid QBs in the league.
For as interesting as statistical analysis makes baseball, psychology, which plays a such a significant role in football, makes that sport just as interesting.