From a democratic point of view, it doesnt even _matter_ whether it makes sense or not. The only thing that matters is whether we, as a society, collectively _want_ private, non-commercial copying (i.e. filesharing) to be illegal or not.
Knowing that "we" probably would make non-commercial copying legal, "they" simply do not let us vote on it. Copyright is basically locked out of any democratic decision process, worldwide. Basically all existing political parties shield copyright away from democratic influence like a sanctum.
Only in the recent 2-3 years, in a number of european countries, people have realized that voting on this issue in the current system will basically forever be impossible and have formed pirate parties focused solely on getting rid of the filesharing prohibition.