I'm sorry to say it but probably 85-90% of the traffic is because of greed.
All those signature campaigns, giveaways, airdrops some sort of "free money", attract more and more people who have come here to "work hard" and make as more as possible.
Although I can (proudly) say I didn't have any paid signature until I was at least Full Member, but that's mainly because I didn't bother to check how it works back then, and I didn't know it can actually pay a decent amount.
There's a good side to it though: signature campaigns mean people are actually willing to do things for Bitcoin, which adds to it's acceptance.