Was it really family reasons? Perhaps, eventually, we'll get enough reporting to put something together; for now, I'll just say that I'm increasingly of the opinion that even the politicians themselves probably don't know the answer. We're talking about multiple variables, with "how much he wants it" only one, and family issues only part of that. So maybe the family was an outright veto -- or maybe if Barack Obama was at 25% approval instead of 50%, and maybe if a few more people were begging him to get in (or, perhaps, making firmer commitments), then his current level of commitment would be enough. As I said, I'm not sure that I'd trust Daniels himself (or any other pol) even if they believed they were being honest about it.
Of course there may be solid, relevant, info we don't know -- Daniels (or Barbour, or Thune, or Huck) could have been told by publicly neutral party leaders that they were really with another candidate, or even that they would strongly oppose him.
And the list goes down. Remaining from my list (as of early this spring) of plausible GOP nominees for president in 2012 are Romney, Pawlenty, Palin, Perry, and Jeb Bush. I originally said my list of eight (it included Barbour, Daniels, and Huck) had at that point (late March) at least a 90%, and probably close to a 98% chance, of winning the nomination. So far the list as a whole is underperforming, but in my view it's still just about as likely that the nominee is on that list, although I suppose maybe a tick or two less likely. Still safely over 90%, at least in my opinion. By the way, for what it's worth, I really don't think Jeb is going to get in -- he (and Perry) are on the list because if they chose to enter, I think they would still be viable.
As for Daniels...I've never thought he was nearly as formidable as some made him out to be, so I don't think this is as big a deal as Huckabee's recent decision. Basically, I never saw what he had that Pawlenty didn't have, and Pawlenty would have had a major head start, among other advantages. Still, I thought he was at least a viable longshot, and apparently that's done now.