I think this is happened because of my first tweet was readed by new twitterers and they didn't know about twitter and how to monetize their tweets. I analogyze Revtwt with Google Adsense in a blog. In 2000 up to 2004 Adsense clicked by many people because many people didn't know what is adsense, and they just use internet to search information and not to get money. But, now many people are knowing about adsense and they want get money from internet so the click probability become low.
So, if you want to get more money from twitter you must search many new twitterers and tweet your ppc ads. Don't tweet too often because that makes your followers bore. This is just my experience.
