The goal should always be to reduce the human dependency - where reasonable which is where all the argument is, because of the cost/benefit analysis.

Mandatory scaffolding for roofing contractors would save some amount of deaths/injuries (and the related expenses) but add expenses to each job.

Some roofing firms refuse to operate without scaffolding; you pay for it or you find someone else.

I don't think the GPs point is about personal safety of workers, but rather critical safety systems that rely on one person with no backups. Like an ATC tower for a busy airport staffed by a single person on an overnight shift.

A painter who does a bad job setting up a ladder is going to have a bad time, a lone ATC operator having a heart attack potentially puts multiple large aircraft full of people in danger...