Disclaimer: I went for a memey title, but hear me out. Also, I want to stress this is a theory, not something I think is reality...just something that could possibly be real. I don't think it's the likeliest explanation, but it's something that popped into my head. We'll see what happens if she drops out today, too.
What this comes down to is the age old question: Is an organization - in this case the GOP - more evil, or more stupid? Essentially, are they running things competently?
They don't seem to want Trump. But they know swapping him out would be a disaster. What if Nikki Haley is a sacrificial cutout to try to dampen the blow? Here's my idea: They're pushing Haley to stay in, precisely because she's hated but, if Trump gets taken out one way or another, they're not going to put her in as the candidate, even if she's still in the race...they're going to swap back to DeSantis, who recovered some of his popularity after dropping and endorsing Trump, and was also polling higher. It would make the whole process seem much more palatable to some. I personally don't think it would be enough, but it's certainly better than running Haley.
Essentially, Nikki Haley is in the race to be hated, so the GOP can stab Trump in the back and swap back to DeSantis or something, and pretend it's for the good of the people and the party.
And, since I know we probably still have some DeSantis fans, I'm not even saying he's in on it in this hypothetical situation. He could be, in one version, but it's certainly not required. Dropping out and endorsing Trump was a fairly natural move, and is in no way a condemnation on DeSantis.
No matter what happens, this election cycle is going to be a chaotic mess. The cleanest option is somehow a Trump v Biden rematch. Anything else gets even stupider, and even less representational.
Not any more evil than anyone else.
They are more malicious. They are prepared to destroy the Republican Party to prevent Trump (who we all no is effectively a reformer) from gaining power because they are so scared of losing power.
Rishi Sunak is an excellent example of what they want from a Nikki Haley presidency. A one term punching bag who will endorse and pass all available Left-wing legislation. Progressive legislation will run the country into the ground, the party will be purged of populist movements (or effectively die), and then the Progressives will claim that they have a unanimous mandate to push even MORE progressive legislation to solve the problems that the faux-conservatives created by endorsing earlier progressive legislation. The 400 year old Tory party may die. It is actually the oldest political party in history AFAIK. And that is preferrable than allowing any other candidates the opportunity to win any possible seat.
The RNC is desperately trying to kill itself to defeat Trump. He SHOULD get the nomination, but I can't promise you he will. Nikki Haley is systematically destroying Republican data integrity by populating it's primary voter roles with Democrats. She is burning all available Republican donor money that would still "vote Red no matter who". She was funding her campaign with RNC funds. The RNC is effectively bankrupt, and we are exactly 8 months from election day. That is why Trump is selling over-priced shoes. He's raising money outside the party to fund himself.
The next step is that if they Republicans can't keep Trump from the nomination, they will lose every available lower seat possible. Same thing happened in Richard Nixon's campaign.
Trump winning the election in a landslide won't mean shit if him and his VP are impeached and removed by a Democratic house and Senate before 100 days into his presidency. Then the house majority leader (who would be a Dem) can be president. The current gambit is to make sure that the Republicans can't win any lower race, particularly in the house, guaranteeing a Dem presidency regardless.
In the mean-time, Nikki Haley is suicide bombing her career with the nomination process, corrupting internal data, bankrupting the RNC's budget, dissuading corporate donors, and doing everything in her power to cause the Republican party to be unable to win this or other elections.
The Republicans are full on: death before victory; because they are the uniparty, and they are scared shitless that someone might fire them from their cushy DC position.