Good question.
My initial thought is that after the Ebonite buyout, it was a fairly easy release for them (previous cover and core) until they could get up and running with newer production.
It looks like the Code series will replace it, but I don't have any explanation as to why another Heist wasn't released. Since the Heist is still on the website as a current ball, I guess there is still a chance that they could release another ball in the line.
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