In order to trade there needs to be, 1) A way to communicate securely. 2) A method for making secure payments (e.g. a multisig system). 3) A rating system for buyers and vendors. 4) A forum for connecting buyers, vendors, and third parties (for mediating multisig).
Though markets help facilitate all this, it seems that it could all be done without them.* So why, then, are markets still so popular in spite of the obvious risk of exit scams and LE seizures? If there are reasons, I would love to hear them.
*At least markets as we know them, with escrow systems and all that, as opposed to a simple forum for posting listings.
I'm kind of in agreement with your sentiment here. A simple forum is really all that's needed (tmg somewhat proves this), and it wouldn't even need to be particularly secure as long as everyone made sure to follow all the proper opsec procedures and only ever used encrypted messages to communicate with vendors.