User blog comment:Jopjopjop/Volume 18 Spoilers/@comment-4547267-20140716020122

Does the Bael head want Issei to be a Maou because he is populairty with the new Devils, or because he need another person? Also it would be weird if the reason was because the Bael want to weaken the Gremory by making Issei a Maou so that he can't get a harem, which most of the girls are very powerful and would make good members for the Gremory. Just a theory.