First of all are there are plenty of free scripts, not only on the SDN also local scripts offer free use.
Now let's imagine you are the scripter...
... you put a lot of hard work into making a script, a lot of time, a lot of effort to push updates and in general keep the script up to date...
... would you make this for free?
And also, imagine all goldfarming scripts would be free?
The result would be a destroyed economy in rs...