It is the middlemen who currently run this world.
Easiest way to make money.
1. Find a product that's valuable.
2. Buy the same thing at a lower price by purchasing in large quantities.
3. Sell individual units at a profit.
The giants Amazon, Alibaba, Costco, Walmart, ETC. all exploit this tried and true method of creating value.
I also sell products wholesale on Amazon and can tell you from experience this works. Anyone can do it.
The thing is, once people can make transactions directly from the warehouse or the seller without the need of a platform or place at the best price and with great shipping, security, trust etc. won't all forms of middlemen become obsolete?
Everything would be cheaper and more accessible.
In a perfect world, we'd have decentralised marketplaces like this as you mention. But honestly I doubt that it's going to be feasible in the near future. I absolutely agree with avikz as well. A decentralised marketplace doesn't necessarily mean that you're directly interacting with the manufacturer.
It'll be hard to disrupt this market due to people's familiarity with dealing with centralised marketplaces. Also, how exactly will the middleman be cut without having holes in the system that is open for exploitation will still need time to develop, imho.
What I think is most likely is that the traditional marketplaces will in fact respond to increased crypto adoption by integrating it into their services further, such as accepting it as a form of payment or even using blockchain as a ledger to keep records. But a truly decentralised marketplace seems like a far fetched idea for now.