From my Washington Post column today:

But there was no point in holding out for more. Haley’s most effective barbs against Trump were about his character, not his policies. That’s not a critique that lends itself to bargaining. Trump can’t credibly promise to embrace fewer conspiracy theories, or to be a completely different person.
It may not have escaped Haley’s notice that, in addition to having nothing to bargain for, she had little to bargain with. A lot of Haley’s voters were not so much pro-her as anti-Trump.