She’s unpopular and would lose.

She was set up to increase her visibility, position her as a next candidate, but does not seem to have benefited from the opportunity

I’m going to assume this is a good faith question. What’s wrong with Harris is that she is essentially polling the exact same as Biden despite not being blamed for inflation, the Gaza invasion, the withdrawal from Afghanistan, appearing senial in a debate, not being old, etc. That is to say that despite having none of that baggage hanging over her head, she essentially has the same chances of winning as Biden.