Why is North Korea so Poor?

Ignoring the obvious explanation of communism why is North Korea as poor as it currently is? If we assume a few things, it just doesn't seem to make sense to me.

Assumption 1. North Korea got enough aid and machinery from the Soviet Union before its collapse that they had industrial capabilities similar to that of 1950's America, obviously ignoring scale.

Assumption 2. The North Korean government has no qualms about simply whipping its population forward and sacrificing all consumer luxuries with a total focus on increasing industrial output.

Assumption 3. The North Korean government also has the capabilities to copy any technology or design ideas from the rest of the world and doesn't care about doing so.

If we assume these three things I don't understand what keeps North Korea from simply brute forcing itself to either a higher standard of living or creating some comically massive military capable of destroying the south through millions upon millions of munitions. The Soviet Union went from being a nearly preindustrial society circa 1920 to building nuclear weapons and probably having the most powerful conventional army on earth circa 1950s under similar circumstances.

While our modern factories and goods are far more technologically advanced than in the 1950s they are still ultimately built from the same raw materials just used in a far more sophisticated manner.

The two simple explanations I can think of are a lack of materials critical to run a modern economy, or that the North Korean government is simply more concerned with supplying dear leader with foreign luxuries and so all the minerals, power, and food are sold abroad for pennies on the dollar to pay for imports. I'm curious to hear what everyone else hear thinks though.