It's because those previous contributions were edits and not posts in their own right.
See the Main Meta article here:
Come Take a Look at our New Contributor Indicator!
The new indicator works by the age of a user's first visible post.
Folks will see an indicator when they go to interact with new contributors (visible for a week following their first post) letting them know that the person is new. A handy link to our Code of Conduct will be in the notification for reference.
This could be a question or answer, and the association bonus won't influence the behavior. While you might not be new to our engine, everyone is new when they first join a new community, so the indicator is shown.
As to why you're seeing this on this site after you've been active on other sites and you presumably know how SE works is subtle.
I think the reasoning is that each site has the capability of having a different personality and have different standards of what's an "acceptable" question or answer - so me jumping into SO and asking a programming question that doesn't have the right amount of background information or context will result in my question being heavily downvoted. The "Black Hand of Welcoming" indicates to other people that I've not posted there before and I might need educating rather than just getting slapped down.
However, I do agree that it can seem somewhat condescending to wear this badge when you're a seasoned pro on other sites.
Your first proper answer was on the 7th, so you need to wear the hand until the 14th.