I've seen the owner of a wreckers and spray painting business crawl under a car using just a floor jack. He was a big boy. I was surprised he did it as he is a panel beater by trade.
I can’t recall the exact statistics, but I recall reading that motor mechanics (and similar) made up half, or more than half, of the deaths and injuries due to misuse of jacks and jack stands. I suspect complacency creeps in after a few times of getting under a car only using a floor jack. And, probably almost 100% of the time they are absolutely fine. It’s that small percentage of cases when things go bad and a car falls on someone when things get really ugly very quickly.
It’s similar in the electrical trades. Tradesmen are a very high proportion of electrocution deaths and injuries.
They should know better, but sometimes compliancy, poor workplace culture, rushing to finish a job, and sometimes it just the old case of “I’ve always done it this way” (and I’m not changing).