For an agent that executes locally, or an agent that doesn't execute very often, I'd agree it's arbitrary.

But programming languages make tradeoffs on those very paths (particularly spawning child processes and communicating with them, how underlying memory is accessed and modified, garbage collection).

Agents often involve a specific architecture that's useful for a language with powerful concurrency features. These features differentiate the language as you hit scale.

Not every language is equally suited to every task.