In today's software world, dozens of different hardware platforms exist. Patches for the PC platform are different than those for Sparc hardware. NT patches for the Alpha vs PC could include a wide variety of alterations. A handful of software vendors learned via trial by fire that a hasty fix is not always a quality fix. Days after the initial bug was reported and fixed, slight variations of the same bug surface days later providing a healthy dose of mud to the vendor's face.
Software companies are often big, and full of internal procedure.
Departments don't always play well with others. Going beyond the lack of appreciation vendors show, there are several other reasons not to report bugs after discovering them. Despite all of this, the technicians at the vendor still could not figure out how it all worked. Up to a year later, the vendor was still seeking assistance in getting the exploit to work. In 1998, the same security company worked with another large unix vendor with a nasty remote exploit that gave attackers full access.