Why Hasn't Gun Gale Wars been Approved Yet?

Manga Guidelines said:
I.3　Submissions Etiquette
Please observe the following when adding new manga to the database. It will help your submissions be approved faster.

I.3.1　Ensure your submission does not fall into one of the following:

• Unpublished webtoons: webcomics released on independent digital platforms which do not belong to reputable publishing companies (e.g. pixiv, Naver). When a reputable publishing company in the country of origin prints and distributes bound volumes of the webcomic, then the published version will be added.
  
• Comics created for markets other than Japan/Korea/China.
  
• One-shots already compiled into bound volumes.
  
• Artbooks, series guides, reference materials, picture books, and animanga.

I.3.2　Search carefully to be sure the manga is not already in the database or waiting in the queue.
Try searching the Japanese title, only one to two words of the title, and known synonyms.

I.3.3　Complete as many fields as possible.
At minimum, you should be able to add a title, image, and at least two pieces of other information (e.g. genres, magazine, status). Entries without the minimum information may result in an automatic denial.

I.3.4　Include links to any supporting evidence for the entry information in the "Additional Info" field.
For example, image of the volume's Table of Contents, link to MAL News, creator's blog/Twitter, etc.

I.3.5　Censor NSFW images following guides detailed in Section II.4.b. Uncensored images may result in an automatic denial.

I.3.6　Do not submit the same addition more than once. This will only serve to slow the rate of acceptance rather than improve it.
If you received an image error upon submission, don't worry, it has been submitted.