First thing a leader needs is people who believe in them. Romney is arguably the most notable NeverTrumper. Romney did not simply attack Trump’s policies, he attacked the character of the man.
“I am far from the first to conclude that Donald Trump lacks the temperament of be president.” Mitt Romney
“Donald Trump’s personal qualities, the bullying, the greed, the showing off, the misogyny, the absurd third grade theatrics. We have long referred to him as “The Donald.” He is the only person in America to whom we have added an article before his name. It wasn’t because he had attributes we admired.” Mitt Romney
Maybe if he apologized, then Trump would consider him?
http://thehill.com/blogs/blog-briefing-room/news/307521-report-trump-team-wants-romney-to-apologize

Romney doesn’t merely disagree with Trump’s personality quirks. Romney believes that the POTUS elect is ignorant and that an implementation of Trumps policies would rob Americans of their bright future.
“Donald Trump tells us that he is very, very smart. I’m afraid that when it comes to foreign policy he is very, very not smart.” Mitt Romney
Romney believes that Trump’s foreign policy ideas such as making peace with Russia in order to defeat ISIS in Syria are ravings of a mad lunatic. Romney wants to continue the world police role for the United States because he views the United States because of his rigid preconceived image of our role in the world, guaranteeing security to the world even if it bankrupts the U.S.
“Let me put it plainly, if we Republicans choose Donald Trump as our nominee, the prospects for a safe and prosperous future are greatly diminished.” Mitt Romney
A Secretary of State is suppose to effectuate the Trump foreign policy the American people elected. In this case, Romney has a totally different vision in this country from Trump, and could not possibly do the job while remaining true to his own principles.
“Frankly, the only serious policy proposals that deal with the broad range of national challenges we confront, come today from Ted Cruz, Marco Rubio, and John Kasich.” Mitt Romney
Romney represents the failed choices of the republican party. A failed presidential candidate who was rejected by the electorate over the last 8 years until Trump came along and proposed a foreign policy based on American interest, not assuring security of Saudi Arabia, Syria and Ukraine. The people are tired of the outdated Romney world view.
“If Donald Trump’s plans were ever implemented, the country would sink into a prolonged recession.” Mitt Romney
Every prediction the NeverTrumpers made to date failed to materialize. There is no reason to take them at their word now.
Dear President Trump, pick somebody for Secretary of state who represents what your promised to the people, like this guy:
Rand Paul
or
Tulsi Gabbard