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).

[1] https://www.politico.com/magazine/story/2019/04/29/lis-smith...