The pushed payload didn't generate any new traffic. It merely replaced the recipient of a crypto transaction to a different account. It would have been really hard to detect. Ex-filtrating API keys would have been picked up a lot faster.

OTOH, this modus operandi is completely inconsistent with the way they published the injected code: by taking over a developer's account. This was going to be noticed quickly.

If the payload had been injected in a more subtle way, it might have taken a long time to figure out. Especially with all the levenshtein logic that might convince a victim they'd somehow screwed up.