1. She got edged out by the likes of Bolton and Pompeo
It's no secret that the national security adviser and secretary of state, respectively, are foreign policy hard-liners. And that while Haley was outwardly very tough within the UN (and the Trump administration), she was reportedly a voice urging more moderation -- and toeing the preferred line of establishment Republicans -- in private. While Haley was, without question, a star of the first year of Trump's administration, she did clash with him at times over, among other things, Russia. During a TV appearance in April, Haley announced the US would impose new sanctions on Russia. Trump insisted no such sanctions had been put in place and the White House blamed the misunderstanding on a "momentary confusion" on Haley's part. She quickly responded that she did not "get confused."
With Bolton and Pompeo as the new shiny objects in the Trump Cabinet, Haley may have seen the writing on the wall -- and decided to leave on her own terms (before she is pushed).
2. She needed to make some money
Haley has spent a long time in elected (or appointed office). Prior to being elected governor in 2010, she spent six years as a member of the state House. Those are not hugely lucrative jobs. In 2015, the year before she was tapped to serve in the Trump administration, she and her husband reported an annual income of just over $170,000. In 2014, that number was closer to $190,000. And in 2013, Haley and her husband, Michael, reported making $270,000.
According to Haley's 2018 financial disclosure, she reported a significant number of outstanding debts, including somewhere between $25,000 and $65,000 in credit cards, a mortgage in excess of $1 million and a line of credit between $250,000 and $500,000.
With one child in college and another headed there in the next few years, Haley could well have been lured by the seven-figure salaries available to someone with a resume like hers in the private sector.
(Also worth noting: Over the weekend, Citizens Responsibility and Ethics in Washington, a government ethics watchdog, requested an investigation into Haley's acceptance of seven free flights from South Carolina businessmen in 2017.)
3. She wants to run for president
There's very little doubt that Haley has her eye on the White House at some point in the future. (Doubt me? Haley brought her most trusted political adviser -- and pollster -- Jon Lerner to the UN with her.) Knowing that her resignation would set off talk of a potential primary challenge to Trump in 2020, Haley laughed off the possibility during her comments on Tuesday -- making clear she plans to campaign for Trump in two years time.
In truth, Haley is too smart to run against Trump in 2020. While Trump's approval ratings are in bad shape with the broad electorate, he is among the most popular Republican presidents ever among Republican voters. No one is beating Trump in a primary in 2020 -- not Haley, not anyone.
BUT, just because Haley isn't running in 2020 doesn't mean she isn't running. Remember that whether Trump wins or loses in 2020, the 2024 Republican nomination will be open. Yes, Vice President Mike Pence is a likely candidate -- particularly if Trump wins a second term in 2020. And he will be the Trump candidate. But what if there is a desire for a candidate who has OK relations with Trump world but also is not seen as totally and completely aligned with a former president who was, to put it mildly, a non-traditional Republican candidate and president?
Enter Haley! She will have spent almost two years serving Trump, yes, but, by the time 2024 comes around, she will be six years removed from the Trump White House. Which might be a very appealing thing for Republicans.

CNNâ€™s 3 theories why Haley left the Trump Administration