There is always more to the story beyond what we hear.
I'm guessing Christie planned to run, but the RNC told him straight out that they could not get behind him with support and funds unless he addressed the weight issue, which no doubt the RNC seen as a huge obstruction to the path for a win.
Lose the weight, we're with you. Otherwise, no deal.
That line about concern for his health and his family is typical political BS.
They plan on Hillary as their competition, and Christie could never win one on one.
The weight isn't the issue, not the number one issue, as misguided republicans might assume.
The issue will be Christie's temper, his tendency to lose it, that will turn off the public.
The turn off for the average voter beyond Jersey, more so than the weight.