Because management thought it would be a cool idea. In the end, wota showed their sense of humour by only voting Nacchan into the top64. Nacchan left pretty .... suddenly ... because of her role in same shady activities with fellow member Yonezawa Rumi. Needless to say, Nacchan is now one of the elite gravure models in the business. And since then, graduates stopped being eligible. So, you could say, one idea that flopped.