why yahoo chat rooms filled with spam bots ?

Yahoo chat rooms is one of the awesome and best designed chatting application in the whole wide world i first used yahoo chat almost 7 years ago and after trying tons of other similar services i think yahoo is still the best in this space but unfortunately a "Product that works" and has a potential to be good "Business Model" and a product that can generate a great revenue is lacking a quality assurance i never thought people at yahoo are so dumb enough to neglect yahoo chat to such an extent and not to forget Orkut lost to face-book because of Brazilian spammers.

I last used yahoo chat in 2006 after 5 long years recently when i tried to socialize on yahoo chat i was amazed to see that 80% of the users was actually a chat bots(spam bots) trying users to redirect to some porn sites, after Pinging about 30+ users i was finally able to chat with a 60 year old man from England who shared similar grievances with me and was telling me that he will soon switch to ICQ (owned by AOL chat rooms) and saying he had enough with yahoo chats.

though yahoo introduced captcha to reduce spam-bots which was not the case when i was using back then, but still i wonder how these spam bots bypass this security step, what ever it is i don't think so there are still many left in yahoo chat team to address this issue what ever it is people are moving to other alternates and another iconic product of yahoo might soon fall apart, its would have been nice if someone (google, Microsoft, AOL) would takeover the yahoo chats just like yahoo search, still fingers crossed hoping yahoo will take a look into this issue.