because, it's awesome.
Skip to 1:20 for the Puck/Rachel question.
Lea: What song would you and Mark sing as a duet? Do you think there's a chance for more Puck/Rachel romance in the future? -Julie, from Kansas
L: You wouldn't like anything that I'd suggest.
M: Oh I don't know. Try me.
L: We could do like, "Lucky" by Colbie Caillat and Jason Mraz.
M: Alright.
L: That could be sweet.
M: That's a sweet song.
M: (laughs) Ah, I loved working with Mark and the Puck/Rachel storyline. I kind of, um, like, begged Ryan Murphy to write it. I was like, "c'mon, y'know. But what about Puck and Rachel?" and he wrote it into the show. And I think that the way that they did it was hilarious. Um, but yeah, getting to work with Mark was awesome.
SOURCE.
*dies*