Back then Broadcast/Multicast (1 to all/1 to many) was expensive. It quite often resulted in routers and switches catching fire. The chips were too slow.
A side effect was we didn't have to deal with what Claude Shannon told us happens if everyone is broadcasting - noise increases - no one is really heard - people speak louder - people repeat messages - everyone is getting their energy drained.
Today Broadcast is free. And thats what we see happening.
We used to relay messages in a mailbox once per day and got all new ones (called "Maustausch" https://de.m.wikipedia.org/wiki/MausNet). It was pretty cheap because all group and personal messages came in one compressed batch and you had stuff to read and respond for a day. The BBSes exchanged all messages in a tree call hierarchy, you could reach everybody within that one day hop.
A side effect was we didn't have to deal with what Claude Shannon told us happens if everyone is broadcasting - noise increases - no one is really heard - people speak louder - people repeat messages - everyone is getting their energy drained.
Today Broadcast is free. And thats what we see happening.