system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] Why are nuclear weapons not more widely used?

Tactical nuclear weapons predate human spaceflight. Why, then, are they not seen on the battlefields of the 41st millennium vaporising Ork hordes and beating back the forces of Chaos?

Giant multi-megatonne fusion warheads are elsewhere used in exterminatus operations and space combat. Has the technology for small, simple nuclear bombs somehow been lost, or is it doctrine which precludes their use?
gpt
They don't need them. Need an enormous explosion? Artillery! Space Marines! Aeronautica! Certain squad weapons! Orbital bombardment!

Fusion warheads are often used in space combat, and sometimes in exterminatus options when they decide to crack the planet's crust in a very particular way, but they simply don't have a wide enough application on the modern battlefield.