I think your vision may be colored a bit because here on HN everyone seems to think that manufacturers can just sell direct to consumers easily by tossing up a Shopify page and letting nature take its course.
The true value of a middle man is connecting buyers and sellers who would otherwise have no idea the other existed, or otherwise facilitating the transaction.
Here's an example that I'm currently involved with. I was approached by someone to create a device that's needed on the market, but doesn't exist. I'm quite capable of building the thing and familiar with the domain, but never knew the thing was needed. Similarly, the company approaching me doesn't have the internal skills to build the device, but they can sell it. The market for this particular device isn't very large (it's only businesses who have machinery that was built using a particular older technology and need to have repairs done), and there are alternatives, so that explains why no one is building these.
In this case, the company that approached me -- the middle man -- has excellent knowledge of the market and its needs and how to best serve them. I, the producer, had no idea this product was needed, and even knowing that now, have no access to this segment of the market, and it's simply not large enough to make it worth my time to begin a marketing effort in that direction. Similarly, the end customers have never heard of me, and have no concept that such a device could even be built.
So there you are, a middleman has just added value by offering to buy something that I otherwise would not know to build, and by selling it (along with other products and services), to a very underserved market that otherwise would be forced to purchase newer equipment they otherwise don't need.