I think Byrne chose McGoorty because Byrne also lived in Northern California at the time and went to the same pool halls. McGoorty might have been an asshole to many but he still had a style and way of speaking that was all his own.
Many, many players were more worthy if talent was the deciding factor. I don't think any other player was still alive, had enough character to make a book as interesting as the one Byrne wrote, or happened to live close to the Bay Area. Byrne is a three cushion player most of all, so that was a big factor I'm sure. He also was around when Ronnie Allen, Searcy,etc...were playing but he just wasn't a one pocket or payball type of guy. Ronnie was a huge personality also, but I think the fact that Danny played billiards was the biggest factor.
I'd guess that he would choose someone like Jay Bozeman as a second choice for a book over any dead legends or great players who just didn't have that strange lifestyle and lingo of McGoorty. Bozeman was one of the greatest players to never win the world title and lived in Vallejo, CA (20 miles away from Petaluma, CA. My hometown and also where Robert Byrne lived for many years before moving back to Iowa)