The are tens of vendors with great DNM history which can be verified via Grams. Most of them required FE anyway, so why they don't just setup theit oscommerce/magento/opencart and sell directly there? That would help decentralization, probably avoid the ddos issue and remove the market fees.
Actually i ordered from BlueViking, he has thousands of confirmed orders and is considered trustworthy as an example. I wouldn't have problems to buy directly from him and i think this is true for a lot of users. We may keep grams for collecting feebacks outside their shops and build a simple search engine which will collect items from trusted shops.
If anyone is interested, i may write a tutorial on how properly configure a server and manage it for the purpose.
Trust. This is pretty self explanatory ... no market = no escrow and no feedback. Well established vendors have already built trust... what about everyone else?
Service, scalability, security. The markets provide all these things (or try to) for buyers and vendors. It's convenient for a buyer to compare several vendors. It's convenient for a vendor to have someone else keep the service running and keep it secure - it may not be feasible for some players to maintain their own site. Do you really want to have a different log-in and password for 20-30 vendor sites just so you can compare the market?