She was a poor candidate
I'm not sure she was a poor candidate so much as she had a poor campaign. She really didn't have a focus or a message or a clearly defined reason why she was running for president. That can be blamed in no small part on a campaign staff that was in over their heads; she used the same people who ran her senate campaign and there's a world of difference between senate runs and presidential runs. She's learned a lot from this and she'll be back in 2024. The GOP will underestimate her at their peril.
She is an amoral stupid racist commie who hasn't a clue how to govern. At least enough people recognized that to get her to leave the stage.