system
Given the following post, respond as if you're commenting on Reddit:
human
[Starcraft]How come you need to research armour and weapons upgrade again on every new mission?

Do the barracks and factories and the like just forget how to make the upgraded armour and weapons? Or do they have to leave the blueprints when they leave. And for the zerg, do the units just lose the upgraded part of the genetic code when the brood leaves the planet?
gpt
When 'researching' better armour and weapons, you aren't actually conducting any kind of research.

Rather, Terrans are upgrading facilities to allow for production of higher quality equipment. Since they typically do not transplant entire bases, those facilities need to be re-constructed for each deployment. 

For Zerg, their genetic code is extremely complicated, and by 'researching' you are manifesting certain higher-biomass adaptations which are typically kept dormant for efficiency reasons. Not even the Zerg can undergo genetic modification instantly, so the manifestation of dormant genes takes time, and is 'turned off' between swarms in order to save biomass.

The Protoss, similar to the Terrans, need to properly upgrade facilities to warp in more complicated technologies. The Psi-resonance of many of their more potent arms and armour interferes with small-scale warp gates, and so the systems need to be modified to properly allow warriors with such equipment to transit from Shakkuras without being scattered to the cosmic winds.