21st Century technology is the same thing, in spades.
You (yes, you personally) can go out and buy a nice shiny new computer for a few hundred bucks. Can you make one (from natural resources) at any price? Heck NO! That requires a huge community of subject matter experts, and an even huger community of folks who want to buy computers.
To make a pocket calculator you need metals, glass, plastic, and silicon.
There are probably half a dozen plastics involved, each with it’s own finely tuned properties.
The case needs to be thin, light, ridged, strong, moldable, capable of accepting coloring agents, it has mineral additives hat make it opaque, surfactants that bind the mineral agents to the plastic, keep the various dry ingredients from clumping, there are plasticizers, and fire retardants.
The buttons need to be soft and friendly to the touch, capable of being co-molded so the numbers are visible even after wear, it needs its own suite of additives, most of which are different is subtle ways from the additives in hard plastic.
The circuit board needs to be a specialty epoxy, it has to be stiff, non-conducting, have a very fine controlled surface roughness so that the metal traces won’t peal off. in needs to survive a pile of processes using acids, metal plating solutions, strong solvents, and accept several coatings, without absorbing anything that could later leach out and damage the circuitry. It needs to withstand temperatures high enough to melt solder.
The chip is encapsulated in yet another epoxy silicone blend that needs to have all the properties of the board epoxy, and be opaque, and flow-able enough to not disturb hundreds of gold wires that are less than a third the width of a human hair during the molding process. And as an extra bonus, the cured epoxy has to have a thermal expansion coefficient close to that of silicon itself.
The display has a liquid crystal, a speciality plastic that changes its transmission of polarized light with applied voltage. It has to withstand vacuum processing, contact with indium-tin oxide (another specialty product) epoxies, and the microspheres used to keep the glass slips the proper distance apart. It has to survive the sealing process. Oh, liquid crystal materials are sensitive to moisture, and need to be protected from water contact from the moment they are synthesized, even the humidity in the air will eventually ruin them.
Each of the ingredients has a limited number of people who really understand the subtle nuances of its manufacture.
One minor example: In the 1950’s Dow corning “lost the recipe” for making silicone rubbers. Why? They were buying all their materials from the same vendors, to the same specifications with the same processes, yet one day they stopped getting silicones and started making only glop.
What happened? The silicon supplier improved their manufacturing technique. The new product exceeded all the old specifications it was much purer. This was critical for the main customer, the budding transistor industry. A major improvement was the reduction in copper, copper is a major killer of semiconductor junctions.
After a year or so of frantic scrambling, they figured out that the old silicon had traces of copper that acted like a catalyst for forming silicones.
There were only maybe half a dozen people on earth capable of making the connection. Suppose 5/6th of them were gone, The remaining 1/6 would be pretty busy trying to do the work of all the missing ones.
So busy that we might not have any silicones for our bathtub caulk (or any other application) to this day!
And I haven’t even touched on all the skills needed to turn sand into hyper-pure single crystal silicon...