Probably because its off-topic? I mean technically it is, and if anyone thinks an ICO is a scam, it should be in scam accusations only perhaps?
Is it really off-topic? Even I didn't know that

Talking about an ICO being a scam in a bounty thread makes it off-topic, doesn't it? It would make more sense for such warning to stick to the ANN thread and its scam accusation topic. Right?
I think scam is so widespread and not everybody go to scam accusation board so it is quite fair that you attack against them in there ANN + Bounty thread.
Nothing should be considered Off-Topic when somebody is giving warning against scam.
Mods might have deleted it because it is just an accusation without a proof. Might be if you included the proof and challenged the tread creator to reply in Scam accusation board then I do not think they will delete it.
The post that is deleted simply look accusation/threat without any proof and I think Mods are right.