Why does my application and Doctor’s sight evaluation form go to the IBGA instead of the USBGA?

That is because the IBGA is our parent organization that officially determines potential members’  sight qualification and sight category placement.  Having a single organization makes every country equal in both placement and approval.  Then the individual countries run their organizations separately for events and tournaments, unless the IBGA is involved in sponsorship of a tourney, where they would again oversee the event with standardized international rules.