Because Alfred Nobel’s will called for the recipients of the Peace Prize to be decided by the Norwegian Nobel Committee, which is appointed by the Norwegian Parliament. The recipients for other prizes are decided by groups in Sweden.
The Peace Noble is political and everyone knows it. (WTF did Obama do in 2009 for instance).
The science and (to an extent)literature nobles are for actual accomplishments.
Thanks for fighting ignorance. I’m from the US and had never heard of such a thing. I had wondered while the caps were kind of pouffy and not squared away for a military cover, but hadn’t wanted to say anything.