My first question would be, why do you need such a natural law? This isn't a rethoric question. Do your setting and game require a specific, hard reason why a digital revolution will and can never happen? Note that this is distinct from a reason for why it hasn't happened yet. Most settings don't need such a specific rule because it's unlikely to ever be relevant. If yours does, nailing down exactly why is the first step to figuring out what the hypothetical rule actually has to accomplish.
I'm not well versed enough in physics to know how intrinsically the fundamental forces are tied to electrical resistance.Very. Not that it has to matter. You are dealing with magic.
Because both I and my players like having a set groundwork to make decisions based on. Invention and creativity are stifled a bit when you have to ask the DM during every downtime "Is lead still 0.41lbs per cubic inch?". I want to prevent a technological revolution, but at the same time I want the players to participate in the Eberron Magitek revolution.
Then my honest advice is to not think too hard about it, say that electronics won't work, and leave the reason vague. Perhaps, recalling that (as other posters have noted) the classical elements are absolutely real things in Eberron, you can decide that the elemental power of electricity just doesn't scale down well enough to enable fine circuitry, but still works fine for things like the levitating lightning rail.
This is my advice because I think if you try to nail down a hard scientific explanation, you are liable to outsmart yourself and end up causing exactly what you're trying to avoid. No such explanation will ultimately hold up under serious scrutiny, and additionally it will be subject to players trying to get around it as real world engineers and scientists try to get around physical limitations all the time.
So, I'd say you're better off not worrying too much about atoms, quantum effects, and all the other small details. Instead, assume
there's an underlying set of laws that work out to "as the real world, except where specified otherwise" on the macroscopic scale. The instances where it's specified otherwise are the existence of magic and the impossibility of an electronic revolution. You do probably still want a rough
idea of why, such as the example above where elemental lightning just doesn't scale like that, because it tells you something about how your world breaks from the real one and provides a hook, but broad strokes like that will be far more useful than worrying about the details.
Since you want this as an excuse to engage with the magitech revolution without having electronics sitting in the background, my estimate is you weren't that tonally interested in including a lot of quantum-scale technobabble in your game anyway. Perhaps I'm wrong.