Why were the N. Mariana Isl. not merged with Guam?

Having developed an interest in the U S Territories due to this year’s quarters, I find it interesting that Guam and the Northern Mariana Islands seem (to the best of my understanding) both culturally and geographically part of the same unit. Was there any suggestion, after the US Trusteeship of the Pacific Trust Territories was being ended, that rather than creating a new territory, that they should join Guam? If not, why not - are there significant cultural differences between the Chamorro on Guam and those of the Northern Islands? Is there any greater difficulty in administering the entire Marianas chain from Guam than administering the Northern Mariana Islands from Saipan?

From Wikipedia:

Huh…guess I overlooked that section. Thanks.