I agree that there should be opportunities for all kids to participate in some type of activity/activities. There is a difference in sports and chorus. If there are two choruses, then they both get to perform at a concert. However, 6 bb teams as mentioned above is a bit much. When my daughter was in jh years ago, they had a no-cut policy for sports. They had 4 teams a-b-c-d. The a and b teams always had games. The c teams did if another school had a c team that they played against. The d teams rarely had games and were rotated in the last spots of the c team. The kids on the c and d teams realized they were not the top players. They would come to practice, but rarely get to play. Maybe it is better to cut and give the kids the opportunity to try somethings else that they would be successful at and get to participate in. Who knows what other talents they might have?
I always thought it was interesting that there could not be cuts for sports teams, yet there were cuts for cheerleading, drill teams, special choruses and bands, etc.
To the OP, I would find out the rationale behind the audition process for next year. Perhaps it is a space/room issue. Perhaps it is a budget cut issue. It is too bad that there isn't a general music for everyone at that age,but there must be a reason. If not, your dd will take the electives and she will survive. Can she try out again for chorus in 7th, 8th grade? Go to the school and talk to the principal. He/she should be able to answer any questions that you have.
Keep us posted as to what you find out.