Why does almost every animated sitcom have that one character that is called by their surname/last name?

I've noticed this trend in some animated adult sitcoms where there's always one character, usually a next door neighbor, who is addressed by their last name or surname. Examples: Glenn Quagmire from Family Guy, Eric Cartman from South Park, Jeff Boomhauer from King of the Hill, etc. Is there a reason why that is? Is it like a rule or something