Troy Smith hasn't started a regular-season game since the 2007 season.
The San Francisco 49ers' commitment to Alex Smith as their starting quarterback has been unflinching. The 2005 first-round choice enjoyed strong backing from former general manager Scot McCloughan and current coach Mike Singletary. He would still enjoy strong backing from Singletary if he were healthy enough to remain in the lineup.
Troy Smith came to the 49ers with strong backing from assistant coach Mike Johnson, who had worked with him in Baltimore. Johnson has gone from quarterbacks coach to offensive coordinator since the 49ers added Troy Smith, meaning his influence within the organization has grown. His support for Troy Smith matters more now than it would have when Johnson held less sway.
I wasn't sure how early the 49ers would turn to Troy Smith if Alex Smith could not play, but the move seemed likely whenever the team felt Troy Smith had spent enough time in the offense. There simply wasn't any indication the 49ers had confidence in Carr to get the job done.
Carr never enjoyed or had much chance to generate the support either Smith enjoyed this season. I also think Troy Smith's natural leadership ability -- his personality -- made him more attractive to the 49ers under the current circumstances. The 49ers need a spark. They also need a quarterback with an ability to operate behind a line that hasn't handled pressure consistently well. While Carr has extensive experience working behind leaky offensive lines, he took too many sacks (never entirely the fault of an offensive line). The Houston Texans' sack totals plummeted once Carr left following the 2006 season.
The Scouts Inc. Insider report on Troy Smith calls him "an ideal backup ... because of his leadership and playmaking abilities" while suggesting Smith hasn't had much chance to prove himself in game situations. The report raises questions about Smith's lack of height -- he is 6 feet tall -- while noting that he is most effective on roll-outs.
The fact that Troy Smith hasn't played much works to his advantage. Singletary is coaching for his job and he knows ownership will not view Carr as the long-term answer at quarterback. Singletary might as well find out whether a younger quarterback can spark the offense and show long-term potential, particularly if he isn't all that excited about Carr, anyway.