Significantly Insignificant said:
Probably because the general perception of guys like Lou is that they are alpha's that don't take a back seat to people. So when they are asked to come in to a roll where they have to take a back seat to others ideas, that doesn't fit their perception and therefore can't see them performing well in that roll.
But then why take this job? Again, we can be pretty sure that nowhere in his interview with Lou did Shanahan ever say "you have full and complete control of this team". Lou knows exactly what job he signed up for, there won't be any surprises here.
Also, Lou is 72 years old, turning 73 about when the season starts. He was just be ousted out of the franchise that he basically created. Is it so hard to believe that he left that situation just a little bit humbled by how everything went down and realizes that he can't be the same GM he was 20 years ago? Why would it be hard to believe that at this tenure of his career he's actually looking forward to a change in pace?