Here's an unpopular opinion - Did he have any other choice? I mean if he had appealed, then people would have said he has no remoarse - just shed a few tears for sympathy and now he is back at it again. What I am getting at is that probably it isn't a big deal. He is only doing what's left to do - simply owning up to his mistakes which defintely seems like the right thing to do - though I agree it isn't an easy thing to do.
After Australia as a cricketing nation was shamed, to me it seemed a bit forced. It might appear like he doesn't accept the fact that cheating deserves such awful consequences, if he had appealed. Their whole image was shattered and so serious that even the PM of Aus acknowledged this. As the leader of the team during that incident, it only makes sense to not challenge it and take it for the team. Leaders are basically at the front line and have to take whatever is in front of their face, and take it for the team.
I agree some people would've been absolutely astonished if he'd appeal. A guy like him after what he's done has to cop some of this criticism and outrage and and admit to it to earn the respect of fans and others. After all, he was the leader of the team, he had power over such decisions. He failed to stop this ball tampering plan even if he had the utmost power in that dressing room besides the other staff.
Admitting to mistakes is obviously never easy to do. Just imagine how shameful and guilty you'd feel while talking about it. Not to mention the criticism from the press/media.
Personally, I feel genuinely sorry for Smithy but he deserved it. Deliberate cheating deserves such consequences even if it was a tad harsh. This apology is just another tiny step forward in redeeming himself to fans and CA. Never a fan of him as a person but respect what he said yesterday.