Years ago I had a ball python that was totally happy to hang out around my neck for hours at a time. Maybe it helped that I had long hair, and some of the time he'd just wrap around with his head in back and snooze to the point where I could completely forget he was even there.
But I got him as a baby when I was 14 or so, and I don't really remember him hanging out comfortably like that until later in high school and college (It's also possible I just don't remember; 14 was a long time ago). My current BP is young and isn't especially comfortable around my neck, but it does seem to get a little easier as he gets bigger.
So it might partly just be a size thing. For a snake that's still young and small, your neck is sort of hard to really get a stable grip on and isn't going to be a very secure-feeling perch no matter how outgoing it is. By the time the snake is long enough to wrap all the way around twice or more, it can get itself into a position that feels much more stable without having to work so hard at holding on.