I think the point of the rule is that seeing the same book nominated again and again and again turns off many members, and it only takes three members to do it. Nominating a book month after month despite the category hoping it'll finally get lucky is sort of a perversion of the process. The rule also encourages people to nominate a book in a month it fits well since it only gets one shot every six months.
But by all means, let's be able to nominate Lolita every month.
