> It's a revolutionary economic argument that specialization doesn't apply to countries
It isn't. The point of specialization is that people can become experts in things, so that not everyone has to be able to do everything. But the goal explicitly isn't for there to be only one person or only one company that knows how to do something -- that's a monopoly, and it's very bad. And if there are going to be a dozen companies that know how to do something (rather than needing every individual at every company to know how to do it), at least one of those companies can be in the US.
> Ore may be much cheaper to mine in another country
Ore isn't really specialization at all, it's resource availability. You simply cannot mine something in a country that doesn't have any. But the US is big enough to have almost everything and even to the extent that it doesn't, it can a) sell mining equipment to those countries that have it and b) ensure that it's more than one country acting as a supplier of those things, instead of allowing a dependency to form on a single one.
> Why haven't other Silicon Valleys and Apple Computers been developed, despite so many efforts?
Apple is an abnormal edge case because in the middle of their existence there was a monopolist (Microsoft) excluding all other competitors while keeping Apple around in an attempt to fend off antitrust scrutiny for their unlawful practices. That allowed Apple to a) invest in designing high quality products while Microsoft was stamping out any other competitors and b) build a strong brand (because the alternative was Microsoft).
To replicate that in other circumstances you have a chicken and egg problem, because you need the scale to have the resources to design high quality products and build a strong brand, but you don't have those resources or that brand with which to achieve that scale. The only ones who do are the other large behemoths, but large incumbent bureaucracies tend to become mismanaged and there aren't actually that many of them.
You also don't want others to replicate Apple, because Apple is a vertically integrated conglomerate. Everyone keeps trying to because they see Apple making a lot of money, but what they should be doing is playing "your margin is my opportunity" and establishing a competitive market where devices are made of fungible components using open standards, because that's how you defeat Apple instead of becoming Apple. It's no coincidence that PCs still have more desktop market share than Android has mobile market share, because the PC platform is still more open than mobile and to the extent that Microsoft has been losing market share it's because they're increasingly trying to lock down the platform and abuse their customers. If you have two closed platforms, the one with more resources is going to win, because then it's Apple vs. just you and Apple is bigger. But if you have an open platform, then it's Apple vs. everyone and everyone is bigger.
> What is the sense of wasting resources on things the country doesn't do well, so some nationalists can ... do what?
Not be dependent on a single supplier for 80-100% of the global production of some important product.