weaponskills count for all weapons?

i played for 100 hours and encountered something just now. i had a mace that had 3 times 20% piercing damage. i swapped it for another mace with lifesteal. now i cleared a well often for shroud relics. i used my twohanded hammer which has no lifesteal. my hammer now does less damage and uses lifesteal. can someone explain that to me.