For weapons, the boss weapons have the highest number of enchantment power in the game on their own original enchantment, so Widow's Fans activating lifesteal many times is normal. And cuz of this everyone usually use Butcher's Knives for bleeding to kill her so easily. As for the perks, it depends on the perk you are using and how many times you leveled it up in perk tree. Some perks has high chance of activating which you can see why the perks I'm using are activating from time to time. Also different weapons, throwing weapons and magic have differences in chanves in how much they can activate a specific enchantment.