Here's the thing, a manufacturer like shimano has to pay for more than just production.
A big chunk of your change goes to pay the teams of engineers and designers that worked out all the details of the crank for the better part of a year.
Then, there's money for creating the tooling. Cold forging anything is very expensive initially, so you're paying for that.
Then there's the labor in the manufacturing and packaging and all the other people that work at shimano.
That still leaves the marketing department and all those teams they sponsor, and the company still has to make a decent profit to continue expanding.
That's all just shimanos cost. Now they sell a batch of cranks, maybe several hundred or more to a wholesaler like QBP. QBP then distributes them around to warehouses, paying for the shipping. They then fill thousands of individual orders for shops, by hand, and ship them to all the shops. They too have a marketing department and office workers, accountants, etc and still need to pay profit.
Then there's the retail outlet that sells to you, which has a higher or lower overhead depending on whether it's a shop or just some guys basement and a website.
The markups are typically 80-120% each step, so say the actual manufacturing cost (not everything else) for the cranks are $100. Then Shimano sells it to QBP for $200 a piece, QBP turns around and sells it to the stores for $350 and they sell to you for anywhere from $400-600.
This is why a place like probikekit, which buys large quantities directly from manufacturers and OEM packaging can actually charge less than what shops pay and still make decent profit margins.
That's what you're paying for. Most electronics and optics manufacturers don't change tooling as often or require as much design work as bike crap. They also tend to manufacture things at much larger scales. Shimanos crank production pales in comparison with say a resistor manufacturer which pumps out hundreds of thousands of items.