It seems like it is like that, I also check the thread on the
Indonesian board and there is no warning. I think because sticky threads have content that generally needs to be followed by forum members whether forum rules (parent rules, parent board rules, child board rules) or that contain information relevant to the forum but all members need to follow. So, even though there was no update or no comment on that thread for long a long time but no warning, I think it is very reasonable.
After all, warnings on old threads are just to reminders, perhaps to avoid bumping unnecessary threads. However, that does not mean there is a warning, it should not be commented on. If something is relevant and doesn't need to create a new thread, I think it would be better to post to that thread to avoid having too many similar threads
Edit: Well I think this is the real reason why warning not showing up
Stickied threads are always in the top of the front page