Well, in my case, with my Dad, it wasn't that he didn't want to see us and be more present in our lives, it was that Mum just made it very difficult, and then married her second husband and moved us away a hundred miles (and subsequently refused to do any drop offs/pick ups). I remember a lot of what she used to do and say, and in later years Dad added some more detail.
With my first XH- big ol' Mummy's boy. Ran straight back up to the Midlands to Mummy and thence on to Scotland, when he hooked up with a woman nearer his mother's age. Just never grew up really.
2nd XH- more present than first XH, but still thinks nothing of booking weekends away (sometimes with the newest girlfriend, sometimes with friends) on 'his' weekends, leaving ds2 with his parents, rather than booking them on his weekends 'off'.
Essentially, at least in the cases of my XHs, it's selfishness coupled with Mummy's boy syndrome. Nothing ever gets/got in the way of their own fun time. Not even their children.