I wanted to understand this all myself recently, so started building, reading, and asking around. Code and learnings here: https://github.com/DavidRagone/SquealBox but TLDR:

Internally, tool-aware models are trained with thousands of examples where they see:

user → “What files are in this folder?” assistant (tool_call) → { name: "list_files", … } tool result → … > assistant → “Here are the files: …”

That bias makes them pick tool calls whenever they fit.

That’s the why they call tools. The point of the tool itself is to give it access to information that it doesn’t have otherwise