And what makes them tick is about what you'd expect: money.
And they get the money by spamming for replies via social nets or IM which, despite all the headlines and warnings and supposed education, continue to run at a "one percent or better" rate.
Convert those to bots and the botmaster has a marketable quantity, one worth thousands of dollars a week (depending on the botmaster's work "ethic" and how many harvesting camapaigns are run) even at a quarter or less per bot.
Cisco's researcher heard tales of botmasters generated thousands a week in income.
How do they do it? Volume!
Fascinating reading, and reminder to tell your people to tighten their defenses and raise their guards against the botsurge.
That quarter (or less) the cybercrooks make is a huge price for your business to pay by having any of your machines co-opted.