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. :-/
Are you serious? If I hack a game and it crashes, it could be for a million reasons. One tiny piece of code is thrown out of whack and the whole thing freezes. The mod SEEMS to be only a number change, but is it? What did the modder have to do to create the tool used to mod it? Did he/she change part of a code that now causes more game crashes?
On the other hand, if Larian adjusts the code, they know what the frick they're doing. So, they can make sure it all lines up right and doesn't crash. In other words, they're not hacking their system. They are the architects. Therefore, unlike modders, they can easily change the number without hacking and potentially breaking the system.