system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU: Thor] The Destroyer was a pretty damned effective weapon... Why wouldn't Asgard just build an army of those to send against dangerous foes (like the Jotuns) instead of risking the lives of their citizens?

I mean, seeing how much damage a single Destroyer did against a small town while battling four of Asgard's greatest warriors, it seems like a no-brainer to send it or an army of it against their most dangerous enemies.

Afterthought: I know they have this whole Honor thing, but it just seems... dumb, when they have the tech/magic to defeat their enemies without the "nuclear option" of using the Bifrost to destroy the planet. If they're so enlightened, it seems like a waste to use their own people as soldiers.
gpt
If they were cheap to make you bet that a paranoid leader like Odin would have an army of them. But he doesn't, so they probably aren't cheap. Odin himself made the Destroyer in comic continuity and it's possible he invested it with a little bit of Odinforce.