Because Skype has all but abandoned Linux. They haven't said ANYTHING about it in about a year, and they're not likely to ever update it.
Moreover Skype frequently crashes under Linux. This is rather annoying. Since Skype has been bought by MicroSoft, I do not expect that things will get better. I am about to switch to Gtalk, since I also use gmail. The only hassle is to tell all my contacts. Before Gtalk was interoperable with Skype, but since Microsoft bought skype, such interoperability might have been suspended. I do not want to fall into such kind of traps. So, bye-bye skype....
Even before MicroSnot bought skype the Linux version was getting less attention, so it's really no surprise that this status continued.
Despite the lack of development, skype works just as well in Linux as it does in windows. Most people I know hate the new skype interface, so I'm glad that they haven't polluted the Linux version with it
I have always said that Windows is no better that Linux, but because the programs for Windows get more attention, it seems that way :