That's because MS never had it ... they (MS) licensed the 'technology' from Sun Microsystems, there was a dispute and Sun told MS to stop using it ... Sun, in effect shot themselves in the foot
In a settlement agreement reached in January 2001 to resolve a dispute over Microsoft's distribution of its Java implementation, Sun and Microsoft agreed to limit the duration of Microsoft's use of Sun's source code and compatibility test suites to support the MSJVM. Because some developers and enterprises have expressed concern about their ability to eliminate dependencies on the MSJVM in the time period originally provided, Sun and Microsoft have agreed to a longer period to permit a smooth transition from the MSJVM.
However, if you really need it, I do not and will not use it, you can get it here ...
Java Virtual Machine
Those sites that still use the MS version better change ... they've got till Sep 2004