A short answer seems to me to be that the use of substances such as gunpowder and explosives have, in Tolkien's Arda, a connotation with evil.
When the reader is first told of goblins in Bilbo's tale:
Quote:
It is not unlikely that [goblins] invented some of the machines that have since troubled the world, especially the ingenious devices for killing large numbers of people at once, for wheels and explosions always delighted them.
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The Hobbit Over Hill and Under Hill
And in
LOTR Aragorn has a singular word for Saruman's use of explosives:
Quote:
'Devilry of Saruman!' cried Aragorn. 'They have crept in the culvert again, while we talked, and they have lit the fire of Orthanc beneath our feet.'
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The Two Towers Helm's Deep
"Devilry' I would equate with Morgoth or Sauron in that context.
Basically, it appears that even the research of such warfare methods is frowned upon by the "good" in Middle-earth, and those who delve into those matters are either evil or heading that way.