Because Zariel would've curbstomped our party without much trouble. As for House of Hope, Karlach wouldn't deal with the devil and wouldn't want us to do that. And we tried with Dammon but failed, Gondians couldn't help us, Steel Watch couldn't do it as couldn't Gortash (if he could, he'd try to bail himself out). I know with all the cheesy options that are possible in dnd we could try more, but then we should ask why we couldn't do the same for all other companions. Or ourselves, why can't we make a deal with some demon or Mystra to get the tadpole out?
Hey now, we stood before Shar and all she did was throw exposition at us while being a massive bitch and giving poor Shadowheart some horrible memories back. I'm sure we'd be fine in the face of Zariel and if not.. a nice game over, like mocking Vlaakith.
Dammon only tried with normal infernal iron. Gondians didn't even try. Combined they didn't try.
Remember, Raphael wanted to make a deal with us to get rid of the tadpole, but he was waiting until we had no other options left so we didn't get a chance to sweeten the deal. However, it never got to that because the tadpole ended up no longer being our biggest concern, so he offered something else instead. You can ask Elminster why Mystra doesn't do anything and he'll say that we don't realize how impactful we truly are. She doesn't want to get rid of our tadpoles because she wants Gale to suicide bomb the Absolute and the tadpole lets us infiltrate.
