As far as the "why" is concerned...
The Bush administration itself kept the lid on this information, due to the fact that these weapons were not "what they were looking for". These were older weapons, and were not being used in combat. Most of the injuries came as a result of exposure during discovery and handling.
The Bush administrative was looking for evidence of an active chemical weapons program. These were not that evidence. They actually added weight to the notion that Iraq had abandoned their chemical Rapids program.