What is so difficult about developing nuclear weapons that makes some countries incapable of making them?

Question

What is so difficult about developing nuclear weapons that makes some countries incapable of making them?

In: 1394

Answer 1

Most of the countries like Mexico, Brazil or the Philippines could build a nuclear weapon in less than ten years if they want it. But there are international treaties and no geopolitical gains to do it.

Submarines and turbofans are much, much difficult to build, though.