What about the broccoli and the brussels sprouts?

Data of a recent study do suggest that among men diagnosed with prostate cancer, a diet high in cruciferous vegetables like broccoli and brussels sprouts may help to reduce risk for prostate cancer progression. However, it needs to be recognized that this type of case analysis, based largely on self-reported data, cannot really be considered as definitive proof of cause and effect. There are all sorts of possible explanations for the association described by the authors.
On the other hand, since a diet high in cruciferous vegetables is (generally) good for one’s health for all sorts of reasons other than the possibility that it might help to defer prostate cancer progression, why would one not want to take advantage of such a diet anyway?