User blog comment:B214/Volume 23 discussion blog/@comment-2804:D41:4A9B:E500:1D4F:A397:BB70:B3C2-20170726041337/@comment-10330822-20170726052708

Because the organization is going to consist of multiple races and species, and Issei has already been to be skilled at recruiting those kinds of people. Issei is very good at make allies across all faction barriers and species, he is the best choice to lead a cooperative group like this.

Of course, they aren't expecting him to lead it right away, they want him to join and then, eventually, lead the group. Odds are someone will more skills as a leader in that kind of work, like maybe Dulio, Tobio, or Sun Wukong, would lead the group until Issei is ready.