One of the reasons Yahoo decided to forfeit its Messenger service is because it's a bit old and it seems they are working on a better platform.
According to the company: “We know we have many loyal fans who have used Yahoo Messenger since its beginning as one of the first chat apps of its kind. As the communications landscape continues to change over, we're focusing on building and introducing new, exciting communications tools that better fit consumer needs.”
They went on to recommend a better substitute to the Yahoo Messenger in firm of Yahoo Squirrel, which is an invite-only group messaging app. Loyal Yahoo fans will be very pleased with this, and also, you can download your chat history to your PC or device for the next 6 months. Additionally, your Yahoo ID can still be used for other Yahoo services like Mail and Fantasy.
It's sad to see one of the first messengers on earth go, but with the newer communication systems and platforms, it was bound to happen.
source: Yahoo Messenger