[scandum]

Most likely for the same reason few people truly understand the theory of relativity, especially the math that is involved.

If theoretical morality is as complicated to grasp as theoretical physics you'll find very few people capable to formulate moral laws. They could pass their practical moral knowledge on to the masses, but the masses wouldn't be able to tell the difference between the real deal and bullocks.

Not to mention that if someone came forward with a solid logical foundation for morality he'd be ridiculed as much as Darwin was when he first published his theories, especially when the conclusions are completely different from main stream religious and political believes.