These “routes” you speak of are mostly pre-common routes, with endings that try to resolve the episode as quickly as possible.
And Baba has said it before. The new route is to make people understand the message that Rewrite is trying to convey, because apparently, most Japanese fans didn’t understand it in the original. So they didn’t want to leave anime-only’s in the dark too.
It’s also smart to do a new route. You can give emphasis on characters from Terra (since the mains from Terra have very little screen time at the moment), Kagari, teasing Moon, and make the story fit anime format without worrying about including all of the other heroine routes in it.