User blog comment:B214/Volume 23 discussion blog/@comment-2208155-20170319171250/@comment-31137559-20170319200631

Well the harem thing might have no bearing because I feel that's something the high-class devils put in place for the new Maou just so it didn't look like they had a lot of power. I know that seems silly, but we can consider that women=status. That might have loosened up now that the high-class devils' influence has waned a bit.

It's stated in EX that Issei would compete in Rating Games, but he doesn't have the time for it. Maou can't participate in Rating Games although their servants(if they are independent) can. And Issei is very busy going around the world to every mythology. While a Maou could do that, a Maou would have to invest most of his time in the Underworld and Underworld matters.

I don't know why people want Issei yo become a Maou. He has never stated he wants to become a Maou or has any desire to. It just doesn't fit Issei. Not saying he isn't smart enough or capable enough, but his personality doesn't really suit him to becoming a Maou. Just let Sairaorg become Maou like he says he wants to.