Sure, why fix the problem (being too easily blamed for an accident when you give aid, etc.) when you can just write a law that does nothing to address it? You assuage whatever societal guilt you might have for the problem without requiring the hard work of actually making any substantive change.

Such a law would be virtually impossible to enforce in any reasonable way; yes, you can make the odd example of someone, but are you going to spend massive effort on tracking down every passerby on whatever surveillance video might exist should they fail to give aid? If you were said passerby, wouldn't you just get away from the scene all that much more quickly to avoid the greater likelihood of being caught up in the mess?

While I disagree with your thinking, I do have to say you're clearly qualified for politics as this sort of logic drives a significant part of lawmaking... certainly in the U.S. and I suspect in other places around the world as well... maybe even India.