It's not an engineering or practical issue, it's a legal issue.
Let's say this "insulated" screwdriver's packaging could be read to imply that it's OK for a user to stick it into a live breaker panel. And now, let's say Joe Bozo buys one, enthusiastically sticks it into a live breaker panel, and (perhaps due to his own negligence) gets electrocuted. It's quite likely that his estate, or his life insurance company, would sue the manufacturer for a whole lot of money, and even quite possible that they'd win, with the rationale being that, as you say, the manufacturer had "tempt[ed] people to work on live circuits."
Now instead, say the screwdriver's packaging said quite clearly "don't do this". It won't have much effect on the knowledgeable user's use of the tool. However, a court would see this as a caution to the inexperienced user, and thus as a defense against responsibility for such a user's harming himself.
For more information, you can look into tort law, most enthusiastically as practiced in the United States.