Actually there was a reduction in all-cause mortality. It's just that the study's design was such that the reduction could possibly have been due to chance. This is not at all the same thing as "finding no ... benefit".

This lack of statistical significance is probably mainly due to the small size of the study (160 men).

Note that the reduction in death rates from prostate cancer was large in practical terms and (statistically) significant.

Prostate cancer kills a minority of men. Take this fact, add in the fact the study was small, and then throw in all other causes of death (which vary randomly) then it is not at all surprising that the result was not statistically significant. This is mainly due to a small study and noise from other causes of death.

I for one am going to keep having my PSA tests.