At Least 13 People Died by Suicide Amid U.K. Post Office Scandal, Report Says

to commit an act usually means that its intentional and illegal. suicide is often neither. hence the passive tone.

compare and contrast: - he committed suicide - he was a victim of suicide - he died by suicide

each implies different levels of legality and passivity, and therefore control, and responsibility.

in this particular case the passive voice is extra important because to any reasonable person the post office management / fujitsu / uk gov are the responsible parties.