Why?
Well ... if i had to guess ... wich i have to, since we dont know.
There was something missing ... either money, or time, or inspiration ... who knows.
Its quite possible they were never even seriously planned in the first place.
Yes, im aware of that datamined content ... but the problem with datamining is that you never know how did that get there ... its perfectly possible that the person who wrote certain dialogue (notice that most exotic races were datamined in same scene) was simply so dedicated for the work, so s/he just included all existing races off the bat ... knot knowing, or caring, if those dialogues will ever be used.
If i would need to point out one thing that would imho be bigest obstacle in implementation Lizardfolk ... its reactivity.
Lizardfolk have completely different mindset from all the other "intelligent" (yes i know this would be an insult for them) races, so while most of them surfice with some special dialogue choice here and there ... Lizardfolk would require such choice in almost every dialogue ... and that would be expensive. :-/
I still dont understand why cant we change Race for our hirelings.
Lets us play Githyanki as racist as they trully are!
