I never understood it either. It was usually silver bearing multicore solder so it had flux, had no issues with flow. The stuff was an absolute joy to work with.
People downvoting this as a joke, it could also bring up a point. Lead acetate was used as a sweetener occasionally in US food products up until the FDA was established. People have been somewhat aware of its poisoning effects since the Romans ("mad painters disease") but still used it in food and water systems. Pretty sure it is still used in some lipsticks as well.
Ah, Hacker News, where you get downvoted for making a joke.
(to be truthful this comment didn't really add anything, which makes it fair game to downvote, but I still got a bit of surprise seeing a decent joke grayed out)