There are several reasons for the law, one major reason is because alot of people think of seals as cute and smart. There are a number of species of seals and I think only 3 or 4 are endangered. One of the laws created to protect them inclued many marine animals. It is a shame because that baby down is the best kind of seal fur for fly tying, it is finer softer and because it is only on the animal a short peroid of time it does not get a chance to dull much.
I have a friend who came across a seal "camp" when on a salmon fishing trip he was able to full up around 4 large garbage bags full of the stuff. This was around 35 years ago since then he has given away dozens of gallon ziplock bags full of the stuff away. The problem is if this was done now even though they are shed feathers you will still get in the same trouble you would have it you got it from a seal that was hunted. It just amazing that this great source that has almost no impact if any will get you in trouble with the law.
Joe