The real answer is because a new model of iPad will be released with the iOS 4.2 release in November. It will have a camera, facetime and increased RAM.
Don't expect it to be iPad 2. Just a model update to quell the competition that will flood the market this coming holiday season. Then again it could well be the rumored 7" iPad. But I doubt it.
http://forums.appleinsider.com/showthread.php?s=&threadid=112958
when will people ever learn? people come up with these "mid cycle minor update" rumors on EVERY apple product EVERY year and it NEVER happens. what on earth makes you think apple is going to bring out a new ipad early when they JUST caught up on demand of the current model? Theyll ride this money train til at least jan-april if not longer.