Normally PhD programs have a timeline of progress. If you don't make regular progress toward those very generous deadlines, you are kicked out.

Neil did not make sufficient progress at Texas. Then he did something weird, where he wasn't ready to defend yet got a postdoc at (iirc) Princeton. Princeton had to rescind the offer because you (ahem) need a doctorate to be post doctorate. Then he got into Columbia's program and finally finished.

He had a lot of hobbies and interests other than astronomy, and he is actually a very smart guy, but it took him a bit longer to get his shit together. I think he's found his calling and is quite good at he does.

I have some sympathy for that because I had a couple advisors quit my program on me and the program still tried to enforce time to degree deadlines on me without asking my then advisor (in a different department by then) and misstating factual information about credits expiring (which is determined at the school level not the department level). I had to get the deans involved.