Can someone elaborate on how community Greed only rules get established?

[Masekase_Hurricane]

Maybe it just late, but I reread this multiple times, and I'm not quite sure what you're asking.
Because the best I can gather is, you're asking "Is there an option to use Need?"
Which I'm going to assume isn't what you're asking.

I think what he is asking is, if everyone can need why doesn't everyone just use need instead of greed.

[Ultimatecalibur]

Its terminology carryover from other games and content. Maps might mostly have stuff that can be "Need"ed by everyone, but the term "Greed Only" for "everyone has equal chance of getting the rewards" is older that the Treasure Map system.

[Claire_Pendragon]

I think what he is asking is, if everyone can need why doesn't everyone just use need instead of greed.

Ah, well the answer to the question then, is an example of my group tonight, which was that the owner wanted some items to be theirs only, so everyone had to either greed or pass.
The owner woudl also greed or pass, but the few items he really wanted, he would use Need. (and if no one else hit need, then he would be the only person to get the item, which was his way of telling us what items he actually needed, versus which items were free for everyone to roll on.)

yes the owner can just say, hey everyone, pass on this item!
But in most cases, someone always hits need, because the chat log filled up with ppl rolling on the gear or something, and missed the message.
Or someone accidentally hits Need, sees the message, and by the time they go to change it, everyone else alrdy passed, and it drops to them.

In short, making everyone use greed instead by default, helps avoid communication errors. (people will still make mistakes anyways)