Because we can't. At least, not well.
Skype has not been reversed engineered for use in open source projects. So this involves using Skype APIs. There are two Skype interfaces, both of which are problematic.
'The desktop API is being closed down: http://blogs.skype.com/2013/11/06/feature-evolution-and-support-for-the-skype-desktop-api/ ""
When the Skype client is running on the desktop it provides access for third party applications (http://developer.skype.com/desktop-api-reference) to talk to the application. This is done via either X11 messaging, or via Dbus.
This is requires Skype to be running and is very limited. It does not provide a lot of required information that KTp really needs.
A two LibPurple plugins exist for Skype, each using the interfaces listed. These are exposed via Telepathy through Telepathy-Haze.
We have added the relevant support into KTp for this Telepathy backend, however in reality due to varying versions of Skype, LibPurple, the LibPurple Plugins and finally Telepathy Haze this does not always work. Research into what versions work and don't, would be useful.
We do not support this, if you have any bugs or problems with the Skype interface, you are on your own.
Skype also have a proper API (https://developer.skype.com/), for use by clients into devices and hardware. There is even a directly Telepathy backend for Skype used by Nokia on the N9. Unfortunately this is not open-source, and licensing of the Skype API even prevents us from making our own telepathy-skype connection manager.
There is a new CM being made using Skypekit. See the presentation here: https://github.com/max-posedon/talk-telepathy-skykit/blob/master/telepathy-skykit.pdf?raw=true
Note how the license isn't specified, legality is ambiguous.
You'll also notice the screenshots are already using KTp. We will support it, but we can't work on it or help it get shipped in distros.
Try and convince your friends to use a platform based on open standards (such as Google Talk). This is why open standards are awesome!