why does stalker's blade lose heal passive when upgraded?

{quoted}

You're slightly mistaken here. Both items give +10% lifesteal vs monsters. Just when you click on the upgrades for Stalker's Blade (Warrior, Runeglaive, etc.) it only shows the added bonus. If you look at the full item, Stalker's Blade - Cinderhulk, it still gives +10% lifesteal vs monsters.

Hope I helped!

its not written on the item though... if it gives the effect, it should be written on it.. right?