It was down to the players being trained in that specific way of playing, I can't imagine Xavi being able to replicate the same thing at Madrid or teams with different styles (other than Spain/Barca), since there wouldn't be as many off the ball movements and outlets in place for him to have that option, he'd obviously still be quite a great midfielder, but he has to adapt his play (and find fewer and fewer outlets), which was part of his problem during Rijkard's rein.
You speak about him being intelligent to not position himself in a tight spot (unlike Modric), as if Modric would do that willingly, it's just part of being a CM in Madrid, the outlets are not as many, and you'll find yourself surrounded by opp. players, now you have to either play it simple (like Casemiro), or release the ball so soon with one-touch passing to safer options (like Kroos, hence his better pass accuracy), or make those outlets yourself by giving more time to your teammates to position themselves (who are not as trained/second natured as in Xavi's case). That's by having the insane ability of not losing the ball, no matter what, breaking through opposing lines, while not losing the vision of your teammates, even if you're surrounded by 3 players, and one of your teammates is making a run far away... that's what Modric does, and what Xavi was rarely pressured into doing, as he usually had more time on the ball in the first place, as well as more outlets and pre-designed patterns.