The God of Alchemy, following Amberser's plan, took action after he fell into Hell, waiting for the moment when the Hell Lords couldn't resist seeking help everywhere, and also leaked information about the God of Alchemy's past.
Devils always like to assume the worst in every action, no need to exaggerate, they would think along those lines anyway.
Amberser didn't expect this reason to be very precise, just barely plausible was enough for them to accept it. Because, they had really lost a lot, and couldn't afford to lose anymore.
For gamblers who had bet everything they owned, along with a seemingly reasonable excuse, there was simply no room to back down.
Everything went just as Amberser envisioned, and upon hearing about the God of Alchemy and Amberser's past, Zariel's suspicion dissipated significantly, or perhaps she convinced herself, at least for now, she decided to try the machine.
Mammon also expressed his agreement, since there was no choice left anyway.
