Because you are. You're looking at it through the prism of culture and history. You're bringing a bias to it that you don't recognize or acknowledge. I read those exact same words and nowhere do I see or read "You no longer have to keep the sabbath". Those words don't exist. Whether or not to keep the Lord's sabbath isn't even an issue in the bible. It's a given that people did. It is a biblical command from the Lord observed by the Lord's people.
Why can you NOT agree with what Scripture SAYS?