Why? Im affraid, you said exactly the reason ...
If you mod something, and then clipping isues come, crashes come, corrup files come, graphical bugs come ... etc. ... its on you, since you moded.
But if this is allowed by creator, people would expect smooth gameplay without any issues, since its integral part of the game. :-/

So if change single value in files can make so incredibly HUGE MESS with the game ... one cant really blame Larian they dont want to go that road, unless they explicitly have to. :-/

I still dont understand why cant we change Race for our hirelings. frown
Lets us play Githyanki as racist as they trully are! frown