Because the tournament is being held in a region of a realm that may not want to have its business entirely disrupted by reams upon reams of inane chatter for a week.
If those in the region who want to join in can simply click a button labeled "enter the tournament grounds" and immediately have access to the tournament chatter, I can see no good reason to force it upon everyone outside the tournament grounds.
To be fair, an event like a tournament should be highly disruptive to the local business. Ever lived in a smallish city during a major festival? Completely disruptive.
