@Patodesu said:

What are the policies behind dividing shows or merging them into seasons? I've seen lots of shows like other animes (Clannad with After Story, Bleach with the new season, etc) that are merge into one and I think it makes sense, is pretty important to have watched the previous part to understand the new one and it kinda completes it.

Our anime guidelines are located here - https://www.themoviedb.org/bible/tv/59f743289251416e71000037#5b71c6b4c3a3684161000001

Having separated parts on MyAnimeList for example causes new seasons of shows to be really well ranked, because only the people who really liked the first seasons and keep on watching are rating them. So I think it would be better to have Naruto and Shippuden together, they are pretty much the same show. Does this type of separation happens in any other show in the site?

Naruto and Naruto Shippūden are already anime merge list. Only Travis can merge the two entries so he will do it at some point, whenever he can.