Because the A64 came out which was the new technology. And to produce two totally different chips at the same time just doesnt make business sense. Especially if everybody is going out and buying the A64
Both the 754 and 478 will stop production soon too. They cant just stop the production line dead as soon as a new chip comes out. But guaranteed, they will drop them soon, in favor of producing the current and future generation of chips.
* Because current socket A motherboards wouldnt support a 4000+ chip, so motherboard manufacturers would need to make new bios's or release new boards (which they wouldnt be arsed to do for a dead technology).
* Because the yeild rates of making Socket A XP processors would probably be crap.
* Because AMD want people to use their latest processors.
* Because the production line for XP chips has stopped. And to reopen it would be just stupid and costly.