Having ten accounts doesn't help you with anything. Campaigns (good paying ones) need max 90 posts a week in average as I can see. 90*4*10... 3600 posts a month to get your ten accounts paid with the max amount. You don't have time to write so many posts.. over 100 posts PER DAY. Even having a secondary account is hard. What is the point? I mean, 10 posts with the main or 10 with 5 accounts.. same thing 
And that is why there is spam. They put in less effort for the same amount of payment. Why wouldn't they do that? It's less work, but the reward remains the same.