Extremely rare diseases and diseases that have no known treatment options are given more lax rules for testing. Without that, there would be no way to develop treatments for them, but it comes with a side benefit of providing a method to attempt new treatment modalities.

Wild guess: it's because he's 65. Many of these severe genetic diseases kill their victims at relatively young ages.

Ethical researchers are thus far being super-cautious about modifying the genome of someone who's likely to have children. While the article doesn't say, I wouldn't be surprised to learn that he has explicitly agreed not to have any (more?) children.

My 2 cents:

a) need to edit liver cells only, not the entire organism, b) the disease is deadly, so the patients do not have much to lose if anything goes wrong.