They seem to be doing just fine with their own thing. I can't think of another developer that has had consistently quality and innovative titles in every generation since the 80s.

Not every business needs to expand into every possible niche. Them not doing so allows for enterprising developers a take their basic ideas and expand on them to get a leg up. The "like {Zelda | Mario | Metroid | Pokemon | Smash Bros }" description is equivalent to millions in free marketing.