system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] If Star Destroyers can be equipped with planet-destroying superweapons, why did the Empire/First Order even bother creating the Death Star/Starkiller Base?

The purpose of the Death Star was to act as a show of force for the Empire to cow the rest of the galaxy with its destructive capabilities, and Return of the Jedi claims that the completion of the second one would spell doom for the Rebellion. However, in Rise of Skywalker, Palpatine unveils an entire fleet of Star Destroyers, all of which have the same planet-destroying capabilities of the Death Star. If planet-killing weaponry can so easily be added to regular ships, and in such large quantities, why was this not just used with the Galactic Empire in the first place? It accomplishes the same task (arguably moreso as if one gets destroyed, you have more superweapons to fall back on), is less of an easy target for enemies to deal a crippling blow, and would probably take less time and resources than constructing an entire moon or planet-sized station to fulfill a purpose that can be replicated a thousand-fold.
gpt
It wasn't easy, and they couldn't even do the "that's no moon"-sized version until they'd been working on the plan for upwards of twenty years, nearly constantly. And even then, they nearly stalled out at the very end. 

Things that are very, very, very, very difficult to do the very first time often get considerably easier the next time, and can even be miniaturized and mass-produced later on.