basically this is a single-hand decision of Moroccan royalty, they do it because they can, and maybe also they don't want to lose their face while losing half of Morocco territory. If you travel there, you'll clearly see even people look completely different in those regions - Moroccans are arabs, these people are africans. their cultures are worlds apart and they really have little in common. one were conquered by the other, recently, and the world just stood and didn't care (at least it didn't end up in usual african civil war with hundreds of thousands dead and millions driven out).

this place is so far not worth any fight for anybody in the west and morocco is playing nice & easy with europe/us.