Why are the bots on my custom map not doing anything?
IIRC from my experience creating custom maps years ago, you need to create triggers for each faction that actually implement the AI type you want them to have. Something like "Always" being the triggering condition, since you want the enemy to always run the AI, and then "Run AI" or "Run AI Type At location" or something similar, and choose the type of Zerg AI you want them to run, such as Easy, Medium or Hard from a dropdown.