I don't see anyone arguing that leaving your signal on isn't safe.
Auto-cancelling tech doesn't work all the time.
It will cancel early when you don't want it to.
That isn't safe.
It won't cancel and you won't know it.
That isn't safe.
You can't just take one use case: "It will eventually cancel" and declare auto-cancelling a safety tech, when there are other use cases that require the user to remember to either manually cancel the signal while traveling through a busy cityscape (where a lot can happen in 20-30 seconds before the auto-cancel tech kicks in), or manually check to see if the indicator is still on as intended when the auto-cancel prematurely cancels your signal.