The decision is in:
" “I’ve decided it is best to give other leaders in the Party the opportunity to become our next nominee.” @mittromney
— Hugh Hewitt (@hughhewitt) January 30, 2015
Hugh Hewitt is too plugged-in with Romney and his team to get this wrong.
UPDATE: He has the full statement here. Key point:
I believe that one of our next generation of Republican leaders, one who may not be as well known as I am today, one who has not yet taken their message across the country, one who is just getting started, may well emerge as being better able to defeat the Democrat nominee. In fact, I expect and hope that to be the case.