Everything by nisio isn't an ln including monogatari. All of his works are published under the normal kodansha label which is a novel label aimed towards 30-40 year olds. That is the main reason but even in terms of content, it's not an LN. No illustrations, lots of pages, bigger paper size, writing level is a lot better than what is aimed for the typical light novel audience, etc. Has a lot of exposition whereas LNs are mostly composed of dialogue (this is why Chitose says that she has a hard time following who is saying what in that picture from twitter in the girlish number thread).
I like watari but I don't think he has anything that comes close to zaregoto :P. (Not to mention, nisio doesn't write light novels either). I think hasekura is still writing Magdala and world end economica. Not as good as spice and Wolf cause he can't economics but lol. Well at least I heard there is gonna be a sequel to the S&W novels though. Don't know when those will be out though.