It's also a venture Nintendo has nothing to really lose by taking. Cuteness/moe is huge in Japan, so the merchandise is near-guaranteed to sell well. It would be easy to export, since Panel de Pon not only has an art style that would greatly appeal to young or adolescent girls, it could also appeal to older collectors who enjoy the cute aesthetic. The merchandising possibilities are almost limitless - the Big N discovered a license to print money 30 years ago when they came up with the idea of slapping Mario's face on everything, so why not give Lip a shot? Maybe not things like shampoo or shower gel or all the other weird stuff Mario got in the '80s-'90s, but stuff like dolls, blankets, curtains, pillows, backpacks, clothing, undergarments, plush toys (ESPECIALLY plush toys <3), all fair game. You could even make gummy candies or noodles shaped like the fairies or even the panels themselves.
I brought up Monster High, which might seem odd, but that franchise is popular enough in Japan to get a series of exclusive web shorts. It's not at all hard to see why either, considering the art design and characters are pretty anime-ish as it is. MH is profitable enough for Hasbro to make their answer to it in Equestria Girls, which is saying something considering how massively popular My Little Pony has been ever since late 2010. By turning Panel de Pon into a multimedia franchise (as opposed to just a video game franchise) along the lines of Mario or Sonic, they could very well unearth a goldmine the likes of which could rival Pokémon in cashflow. Well, probably not Pokémon, but it's a nice thought.
..So why aren't they?