If any trainer were allowed to challenge Hoenn gym when they're ready, it'd be like Jotho suituation currently. If all new trainers were allowed to challenge Johto, so many rage quits. Each subsequent region has a higher standard than the previous, and many trainers say they love Hoenn so much and only want to be in that region. The badges thing is goo for challenging another regions gym. You did need all 8 Johto badges to challenge Kanto gyms in GenII games.