Mostly this: targetting the metastatic process (that is the dissemination of cells originating from the primary tumor) is in most cases irrelevant because a) in the great majority of cases of cancers that will eventually lead to death, the diagnosis occurs when a tumor has already metastasized. This approach won't cure pre-existing mets, which are generally responsible for the lethality of cancer. And b) if you don't have mets yet, in the vast majority of cases, surgical removal of the primary tumor is the obvious solution. The only application that I can see is if you have a non-metastatic tumor which is not operable. It happens but is certainly by far not the majority of cases. So implying that you might stop 90% of cancer deaths is just plain wrong.

There are additional mechanistic reasons but I think that alone is sufficient to relegate this process quite low in terms of likelihood of sucessful prevention of cancer-related death.