supply chains only exist BECAUSE of the 30% markup at each step. In manufacturing business the "rule of thumb" is that items manufactured follow a rule of 3's. If I dig up $10 of iron ore and make it into metal bars then I would expect to sell those for $30. If I have a company that takes the metal bars for $30 and makes widgets I would expect to sell those for $90. Finally somebody would paint the widgets and assemble them into a finished product for $270. That's why Auto parts are so expensive individually versus assembled into a finished car.
That is just about what you see in the retail market. If you go to Home Depot or your local Metal Bar shop and start buying metal bits, you will see the prices marked up the same as if they were included in a retail product so assembling a finished product from Retail parts ends up being almost as much as finished furniture from a furniture store.
Either way you go at it, the world goes around from people that get their 30% moving things from raw materials to your door. Anybody saying something else is trying to monopolize one layer of the chain and take somebody's 30% for themselves.