Why do people only discuss flow heating vs gas heating? In Switzerland I never saw either of them and only know warm water boilers my whole life. I freaked out

Why do people only discuss flow heating vs gas heating? In Switzerland I never saw either of them and only know warm water boilers my whole life. I freaked out seeing electricity going into the bathroom in Thailand, where ungrounded homes are common. Are boilers that uncommon in the rest of the world?