Wait. That line is why you don't want to buy the game? A single line of dialogue. In a Kirby game.
Even if the story is why you don't want to buy it...I...Epic Yarn's storyline was better than the story of SqSq, WWDB, KDL, KMA, KCC and even MWW. I'm saying this, and I have kind of built up a reputation for being harsh on epic yarn for some strange reason.
On top of that, there is literally no Kirby game to date with a story that is actually well-written. Some are displayed well or paced effectively, but even then they're games like RoMK or K64, where the story really is just "Kirby goes to this place, then this place, then this place, in order to carry out a relatively simple goal. Epic Yarn was a good game. Not a fantastic game, or the best Kirby game, but definitely a good game, and I feel like it was most certainly worth the fifty bucks I paid for it, let alone the 25 bucks it's probably worth now.
I dunno, I'm not gonna say that you're wrong for not buying it if you aren't interested, but saying that the story being bad is why you didn't buy it is just...pretty much the worst reason to not buy a Kirby game. Or really a sidescrolling platformer, since it isn't...well...anyway...
After saying that, I'll go on to say that KEY has some of the lowest replay value of a Kirby platformer, since there really isn't much incentive to go out there and collect everything after you've unlocked all the bonus levels (furnishing kirby's yarn house is not my idea of fun), that it doesn't play like a Kirby game, so if you are really big on the float/inhale/copy gameplay I can understand wanting to skip this one, and that the lack of difficulty (regardless of what people try to say to the contrary) really does hurt the game, even if it's in the Kirby series. And all of those are very legitimate reasons not to want the game. The story being bad? not so much.
Well not just that one line. Actually all of Meta Knight's lines in that game. Though I am slowly getting over it and thinking about getting it. Kirby's cuteness can overcome even the worst of details in my opinion.