If you did that you'd need to restate the rules repetitively, and different people would set slightly or dramatically different terms.

Simple protocols for conducting these exchanges are useful because they can be argued about until optimal terms and processes are agreed by the widest group of people, and thus rough consensus reduces friction. Basically people know what to do and what to expect without needing to read the entire post, and if one party deviates from the protocol and there is a mix-up that results in loss of funds they can't claim that the other party was wrong, whoever deviated from the terms of the territory is by default in the wrong.