49ers vs. Bengals – Call timeout!

I have a saying I like to use.  “40 seconds saved on defense is 40 seconds saved.”  Why do coaches like to save timeouts for the offense when they need to save as much time as possible and nothing saves 40 seconds like a timeout used on defense?   On offense, a team will get a play off in much quicker fashion than using the entire 40 second play clock, especially in the two-minute offense.  What makes this situation stranger is that the Bengals called timeout after 2nd down to stop the clock but not after 3rd down.  The Bengals were trailing the 49ers 10-6 with 3:54 left in the game.  The 49ers had 1st and 10 at the Bengals 32 after an interception.  On first down the 49ers ran the ball.  At 3:11, they ran it on second down and the Bengals used their 2nd timeout to stop the clock with 3:05 left.  On third down, the 49ers ran the ball again.  But the Bengals didn’t call timeout.  The 49ers finally called timeout with 2:21 left to setup a FG which gave them a 7 point lead.  Why didn’t the Bengals call timeout after 3rd down (there was an injury on the play but the game clock started after play resumed), especially since they called timeout after 2nd down?  I wonder what was going through Bengals Head Coach Marvin Lewis’ head.