There's always a bunch of candidates who seem credible but can't get enough support, and others who do.
Compare Yang, Williamson, Klobuchar and Buttigieg and a bunch of other candidates. Buttigieg started polling well, which justified coverage. Klobuchar didn't get any coverage until her outstanding debate performance and then her polls picked up.
The others just never polled high enough for anyone to consider them credibly able to be nominated.
[1] https://www.politico.com/magazine/story/2019/04/29/lis-smith...
Klobuchar was getting lots of coverage, including major media endorsements (like the NY Times, which did a weird split endorsement of her and Warren), before the debate performance, and even after she's still barely registering in the polls nationally, polling at around 5% on average
And why do voters feel as they do? Because his weirdness is possibly the result of underlying genius, while for her weirdness it’s more likely to be mental illness.