Identifying environmental cancer-causes is hard & controversial because of 2 main reasons. The first is that, while there are many environmental factors that are known to be unhealthy, it is hard to document whether they specifically cause cancer or not. The second reason is that there are so many environmental factors that people suspect. Combine that with the fact that everyone’s genes respond differently to those factors, and we conclude that it’s impossible to chart every single environmental factor. So we simply focus on the leading & most-affecting environmental cancer-causes in order to treat the majority of people first.