system
Given the following post, respond as if you're commenting on Reddit:
human
[Dune] Why could they never clone the worms and their spice? What made them so different?
gpt
Nobody really wanted to try for a long time; that the worms produced spice was not common knowledge. Trying to clone a sandworm would, to most people's understanding, just give you an uncontrollable and almost unkillable pest. But there are technical barriers as well.

The worms, despite being incredibly resilient as individuals, are actually very fragile as a species. They are extremely intolerant of anything except extreme xeriform climates; if it rains *at all* in a given desert, then imported sandworms will not survive. During Paul's reign, dead worms were found even in the deep desert, poisoned by the increased atmospheric moisture from relatively modest human terraforming  activity. Arrakis is virtually the only planet that is both dry enough but still inhabitable to support sandworms, and that is directly related to the second reason that they've been impossible to cultivate offworld:

You need *sandtrout* to get worms; they reproduce until they've encycsted enough water to xeriform a planet sufficiently for sandworms to thrive, at which point some of them mature into sandworms and start producing spice as a byproduct. Sandtrout are also remarkably delicate; they're prey animals and can be killed by a "five-degree change in temperature."

Sandtrout were unknown (well, the Fremen knew *of* them, but not their importance to Arrakeen ecology) until the elder Kynes; after Kynes, their roles was a matter of absolute secrecy among the Fremen and Atreides royal family to maintain the Arrakeen spice monopoly.

As to why nobody synthesized melange, it's the product of an alien biochemistry (worms are actually theorized in-universe to be either a pre-Jihad experiment or the only recognizable product of a non-human intelligence) and difficult to study in the wild. It's only found on the deadliest planet, occupied by the most dangerous people in the universe who are utterly committed to secrecy, and occurs in a species that lives dozens of meters underground and is impossible to capture.