Because they need to get the materials, which the PhDs in the experiment didn‘t have to, since it was all hypothetical.
And because all the other countries actively work against you getting the bomb.
And because all the other countries actively work against you getting the bomb.
The calculus is not simply 95% brain drain so 5% not drain so 5% will behave in this way. There is correlation between being in each group.
Or perhaps that supports your point. The smart people with fluid morality are vacuumed up by the Metas of the world, leaving none that would build a nuke for a third world dictator.