It's hard to design systems that punishes players and still retain engagement. I believe this is why tadpoles ended up being all kiss and no curse, or now just change your appearance. Just the assumption alone can be a huge deterrent, and the initial narrative is essentially echoing that in that it's rooted in "finding a cure" for the tadpole before you turn into a squid. That + suspicion of the emperor was more than enough for me to pass on using any of them.
From Larian's PoV, you spent all of those resources developing the illithid powers and hamfisting it into the story, unsurprising they made it consequence free and I think the only reason there isn't more obvious encouragement is it would undermine the entire foundation of the story
The Witcher had plenty of engagement, as did Cyberpunk 2077. You could totally screw yourself into bad endings. Hell, Takemura was an immensely popular character, and pleasing hm meant getting a bad ending. In Witcher it was also easy to get the ending where Ciri dies by doing the obvious, popular thing.
None of those games caught flak for the consequences, they may have done for other reasons, but not for having real story divergence based on choices.
