You're not supposed to be able to patent 'Mathematics' or 'Nature' because these phenomena are 'discovered' and not 'invented'. You can patent a device that exploits a natural phenomena but not the phenomena itself.
Unless an algorithm is observed in nature, I don't really see how it makes any more sense to claim it's a natural phenomenon than it would to make the claim of a machine.
There are a lot of bad software patents. Many follow the formula "abstract mathematical concept, but now it's on a computer". For a long time, that's all that was required.
The problem with that is not the math, it's that it's basically the same as patenting "elevators, but yellow" after elevators have been patented. It's not novel.
Why is that notable?