Buttigieg has to realize that the shrillness emanating from the Harris/Warren/AOC wing (coincidence they're all women? perhaps, one could also look at Schiff/Swalwell/Lieu for male examples) of the party is a non-starter with most people. Who are the leaders of the 2020 primary polls right now? Biden, who's always been the pragmatic politician type... Sanders, who may be a lefty kook, but he's an OPTIMISTIC lefty kook, dagnabbit... and him, which is remarkable considering how much better-known Biden and Sanders are at this point. When a lot of Democrats see Trump as a nut, they assume they have to be as nutty or nuttier than he is; this guy at least acknowledges there is opportunity to be had in looking sane.
Besides, homosexuality is chic these days, as the article alludes—in an era where the Democrats are pushing for token minorities and women, being gay affords Buttigieg diversity points he wouldn't have if he were in the closet, and cool points with millennials and Gen-Z'ers who've been hard-sold the notion that gay relationships are "totes adorbs" for about a decade now.