Is there such a genre where the main gameplay focuses on writing bots

Nerf has it's own wiktionary entry (with the meaning "to water down, dumb down or especially weaken, particularly in the context of weapons in video games").

Etymology From the Nerf brand of toys designed as non-dangerous counterparts of existing things, such as sports balls and guns.

Once powerful skills, tactics or strategies that have been rendered significantly less effective by changes in game mechanics are said to be "nerfed", as these once potent weapons have since been rendered as powerful as the foam toys.

Games where you control a group of characters, and have to consider what to do with them, what tasks to assign, etc. come under "Strategy". From here it splits off into "Real Time Strategy" and "Turn Based Strategy" based off the structure of time in the game.

When you control a more dynamic, artificial group, where you do not have as much control over their actions, it classifies as a "God Simulation".

In general, games where it is trying to replicate a certain environment using a deliberate realism are often classified as "Simulations".

I would classify Virtual Villagers as a God Simulation. While there is strategy to it, and you have control over the characters, there is still a loose sense of simulated realism and artificial intelligence to it.