Incarnates don't lose taunt. They simply don't get access to their taunt on their spawn round in which they're summoned. Their next round they do have it.
Not sure where you're seeing this. I just did a test to make sure I wasn't losing my mind and I never see taunt available.
My incarnate has all three infusions and as you can see only has 7 rounds left as this is the third round. Still no taunt skill.