Because Google bought Meebo and then Google decided to get rid of it. GirlsAskGuys did not intentionally abolish it. I'm pretty sure they are going to get some other form of chat available though. I'm not sure how long it will take but I've heard they are looking into their options.
Google bought Meebo and closed it down. They are planning on releasing their own Meebo like chat function.
You know what I think - Google didn't like the competition with Meebo. It was getting powerful like a lot of people used it and a lot of sites had it too. So Google being greedy decided to eliminated their nemesis
I believe the chat service wasn't being funded and essentially dissolved... As to why there hasn't been a new one so far? I've heard that quite a few people don't miss it as they get harassed by other users or female users have guys trying to talk dirty to them. They may bring it back in the future although I don't know if it'll be a group chat or just friends list.
As far as I know, the didn't exactly abolish it. I believe the chat service went under a new owner and they didn't offer it anymore and as such it couldn't be used on this site anymore. Or that's how I've heard.