I don't think mass media is justified to some degree basing their coverage off polling until the primaries start.
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.
Buttigieg's positive coverage started when he was polling below 2% (even when he was polling below 1%). A lot of it had to do with having the right establishment connections[1]. His success in the polls seems to be the result of the media deciding to give him a lot of positive coverage, not vice versa. The same seems to be true of other candidates this cycle (like Klobuchar and Warren).
> Klobuchar didn't get any coverage until her outstanding debate performance and then her polls picked up.
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
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.