This comes from a Gamasutra interview with NLG co-founder Jason Carr...
Have you thought about working with anybody else?
Jason Carr: We have worked with a lot of other companies before, and we're super happy with our relationship with Nintendo. There's no reason to look anywhere else. They keep giving us better and better IP to work with, and as long as we do our job and make good games for them there's no reason for us to venture out.
Because we're still a small shop. We're under 70 people. We like that size. For us, we're like, why would you want to go and talk with these other guys? What's it doing for your business? The guys in the company are just really, really proud of the company and proud of the games they work on.