Why do some Twitter accounts retweet other accounts?

[Justin]

A really weird thing I find on Twitter all the time is Twitter accounts like the parodies, Guy Codes, and things like that, for some reason always retweet other accounts that have links to ChaCha.com. They also all tweet the same jokes. It's so weird. I don't know what ChaCha is doing, but can someone explain? Or am I the only one that sees this?
But why ChaCha? What is with ChaCha? And it's not like they just tweet each other saying "go follow them", they retweet them five times in a row, or post a link to "you'll never believe what this is.." and it links you to ChaCha. WTF?

[eleana]

They are just advertising one another, to try and get more followers. It's sooo annoying! Also they can get money out of doing that. Tublr is better mate haha

[Boss]

To get more followers.