Because they're a bunch of bleeding hearts who have nothing better to do. If one commits an act they are responsible for the consequences thereof. Claiming to be "mental" does not change that fact. Granted there are a few people (>1%) who do not have the mental capacity to understand what they've done, but too many people try to use the "mental" card simply to evade the consequences of their actions.
I don't understand supporting her or the one's claiming it could have been them. Almost $1M has been raised for this woman. She did not snap and do it, it was planned and she knew it was wrong.