Hi - some people prefer not to get repeated notifications for things like this, so the default is that people have to opt in rather than out of watching. If you forget to click the box while commenting, you can always go back to the thread and click "Watch this discussion" under the first post in the thread to get notifications. Hope this helps!
yes I'll have to remember to click "Watch this discussion" , I think lately I didn't receive notifications when checking the box under the comment. thanks!