This is because of two reasons primarily;
1). Invasive species biologists (i.e. Rodda and Reed of the U.S. Geologic Survey or USGS) who see and want to secure continued funding, additional grant money or otherwise have a financially vested interest in adding these 9 species to the Injurious listing of the Lacey Act. By listing them as "injurious", they get to be able to continue "studying" the python problem...
and
2). Radical animal rights groups (such as the Humane society of the United States; H.S.U.S), and some extreme environmental orgs that in essence have an anti animal ownership and use agenda that would like to see an end to keeping reptiles and all other exotic animals. They see it as slavery or exploitation. These orgs use the false arguements of public safety and health and analogies to animal hoarding and other scare tactics to demonize herpetoculture and reptile keeping in the public eye. Although not the initiators of this rule making, they are adament band wagon riders for any sort of legislation or rule making that restricts animal ownership in any way...