The behavior of non-isolated async functions used to be to run on the caller context; then in SE-0338: Clarify the Execution of non-actor-isolated async functions it was defined that we force a hop off the caller's executor -- the proposal explains the rationale. It may have "over-corrected" but the rationale is explained there.
The currently under review SE-0417: Task Executors brings back control over this to users -- a task may specify a preference and be sticky to some task executor.
The snippet you share also doesn't really work under these rules -- because it IS an actor isolated function, specifically isolated to the @MainActor -- so there's nothing to inherit since there's an explicit requirement that general() must run on the main actor.