Why should I write all these systems myself? I don't have the time, skill, or desire to do all that. Larian has all the systems written and thoroughly tested, so why shouldn't I just use their code for myself? Obviously if I wrote everything, I'd understand it all much better, but I just can't spend me energy there. Scripting all my quests is going to take me long enough.
I could forgo the systems entirely I suppose, but I'd rather have it so if you attack someone, they warn you and then attack back. If you steal something, people berate you and then call guards. And if you give someone extra money, you can increase their attitude. The main campaign script does this all, so why reinvent the wheel?