Promotions have been dismal this year, so there's a backlog of candidates across all levels that will eventually need to be promoted next year (else they face losing a lot of employee morale and trust). So they will need to fill the bottom ranks through grad recruitment. It's also common practice for big 4s to establish a presence on campus regardless of whether there are positions. I know of one case where a MBB were not hiring, but still garnering interest from grads for the sake of appearances.