I suspect Pops pushed this on Hunter so he could pad his resume to run for public office. The Navy was told to look the other way.
https://www.washingtontimes.com/news/2019/dec/30/hunter-biden-file-brief-navy-career/
Yes, Joe did try, but to even get to say Hunter served is disgusting, he was given a part time job for 2 days a month and couldn’t make it passed in processing.