I can see some of the reasons being:
- All players have the same rights, all players can pick any starting city.
- First player to pre-register has the highest chance to get the right city picked that the association wants. If the chair is unavailable, this chance may be missed.
- The members in the association can discuss where to start the next round, at any time before the pre-registration starts.
- Associations pick their members, and if they happen to pick someone who is there just to pick a wrong starting city ...well that's on the HR policy of the association.
- Starting city can be changed if someone picked a wrong one, as long as you are in contact with that player.
- Default starting city would mean certain associations would always hold the same cities by default. That's not really an option imo.