That's weird. It's more expensive to get the shorter plans.
If you only have one game you want to play and you're only going to play that game for a month, I can see it. I was tempted to get their online service for Smash. $4 or whatever vs $20.
That's the whole problem. Nintendo wants people to stick around for the long haul but, according to the article, people are opting to play a little now and never coming back. There just isn't the incentive to invest in a year, as cheap as it is. I'm far from poor but I see no value in their online offerings, yet--and I LOVE Nintendo!
Meanwhile I'm about to reach my 12th consecutive year with Xbox Live.