The old saying goes, "You can lead a horse to water, but you can't make it drink." The best you can do for your affiliates is to remind them in your weekly team mails about the VPs that are available. Explain to them that by the end of the month, they will add up to increased commissions and rank. It helps to do the math for them so they can see the numbers and that will help them understand why they need to stay active.