Correlation does not imply causation. You may find that many of the best pool players come from the Phillipines or Canada; you may find that they all stay in hotels; that they all drink coffee in the morning; that they are all right handed...
That does not imply that to be one of the best you must move to Canada or the Phillipines...
Gambling can be a habit. Some of these people just want to gamble.
You can get plenty of mental pressure by playing tourny's and leagues.
That's right. The notion that they do it because they have to, but don't really like doing it, is pure melodramatic hogwash, plain and simple.