It has little relevance but it is relevant if a candidate is claiming another has stolen valor.

The pre politics career of a candidate absolutely matters. Whether it’s military or otherwise.

It’s just weird for the right to chose this fight as they are hopelessly outclassed.

There are many military members and their families in the US voting. Their career is as relevant as anyone else’s. People on a position of power within the government though means you may make very direct life and death decisions for military members though. So its a comfort to many of them if they see you served time yourself and aren’t a tragic hypocrite.

Tldr: It’s relevant to the people it’s relevant to, which is many.