CARCINOGENICITY TESTING can be complex and it often takes long periods, decades, for carcinogenic effects to be shown in man; short-term animal studies, and in vitro tests with bacteria, are virtually meaningless. This lack of meaningful studies, and the will to test, and a budget for testing, have contributed to the differences in opinion.
https://www.bc.edu/dam/files/schools/law/lawreviews/journals/bcealr/27_3/02_TXT.htm