Mafia: general discussions.

Kosh simply didn't find herself in a situation where a dead chatterbox hindered her team, when, according to the rules, he should have been silent.
As for earning immunities, it's not that great either. Sometimes, the first night passes without any killings anyway, and if there are many immunities, it becomes even easier for the protectors and healers to disrupt killings on the first night, and it's not good to sit out the first day without killings and clues. And there aren't any achievements that would warrant giving an immunity.