I think the point is that true diehard fans are made through the hard times, not just the good times, so winning a Cup the first year of existence sets the bar super high, with nowhere to go but down, and that fans who love the team this year because they're doing so well might be in for a letdown/reduced interest if they do less well next year, which is very likely. I can remember cheering wholeheartedly for teams that lost in the playoffs (especially in the final round) that made me feel close to that team even in defeat. In 2011 when the Vancouver Canucks lost in the finals to the Boston Bruins, I already didn't like the Bruins, but I hated them even more after that. This February, almost 7 years later, there was a player on the Canadian men's Olympic team that the announcers kept saying was part of the Bruins Cup winning team of 2011, and I kept saying (yes, out loud)

to stop talking about it, because it just made me cranky. I will always remember that loss. I will always cheer for the Canucks. I will always hate the Bruins. That's how fandom goes. Vegas is missing out on the "suffering together" part of fandom....though I'm sure their turn will come. It happens to all of us. There are just more painful years for some teams than others.
I don't know if that helps, bookworm, but that's my interpretation of the article, based on my experience. Maybe not everybody has moments like that, but I have a few!