Larian Studios

So… as described by Astarion, if a vampire spawn drinks the blood of their master, they become a true vampire. So why is it never an option for him to do exactly that if he wants power? I guess the upside to being an ascendant is walking in the sun but it seemed like it was more for the power. It would’ve made sense to be discussed as an option lol.

Because Larian doesn't want this to be possible so they ignore it.

Lore is mixed in different versions of DnD, but generally, the big key is that the spawn has to be allowed by their master to bite / draw blood from their body. Cazador didn’t consent, so no release from spawn-hood to full vampire.

It helps to think of vampirism more like a contract than a disease.

It shouldn't matter as long as the tadpole allows Astarion to ignore his master's commands. The vampire blood doesn't magically change its properties when the vampire says "I give you my permission".

The truth is, it would be very inconvenient for the devs to make the third option for Astarion, as it would require much more work and it would destroy the narrative choice they designed for him. Becoming an evil full-vampire wouldn't be evil anymore, as it would be enough to drink Cazador's blood. No moral dilemma, no signs that the choice to become a stronger vampire is the evil path - and this is what the wanted to do with almost every companion - evil and good final choice.