LAN, meet WAN, with minimal supervision
And Ethernet makes it easy!
So take a protocol intended to run on a LAN, where damage could be limited to the number of devices drilled & tapped onto a chunky coax. Then came bridges, switches and routers, and of course broadcasts.. Which were (and still are) pretty much a caveat emptor thing. Broadcast storms can and will happen, and can now go global!*
But that's ubiquity for you. Ethernet's everywhere, even if it's not very good, and broadcasts are a cheap way to flood messages to every Ethernet device on the network that may or may not care (hello, Microsoft!).
*Way back, we developed one of the first Ethernet WAN services. And sales being sales, and mostly used to Internet stuff wanted a 95th percentile billing model. Which got some pushback, but sales being sales didn't understand the implications of broadcast storms generating lots of data, and disputes would be a PITA to show the traffic was due to customer misconfiguration, and thus billable. And sales would have to explain the invoice, and suffer any clawbacks of their commission. Luckily we convinced them to drop it after working out just how much it'd cost to try and bill this feature, and it'd be coming out of sales/marketing's budget.
Biting the hand that feeds IT
