We experienced something similar. DD was in year 3, so aged 7 I think. They were allowed to 'audition' for the school choir. All her friends got in and she didn't. She wasn't a hugely talented singer, but she could hold a tune, and was no worse than the other kids. She was already being bullied and this was a further knock to her confidence, plus it meant that she was alone at lunchtime while her friends were in choir practise.
I went to ask politely if there was any chance she could join the choir, thinking perhaps if they knew how eager she was, she would get another chance, but there wasn't. I was given lots of reasons, one of them being something about entering competitions and only being allowed to enter a certain number of children. They didn't enter any competitions the whole time my DC were in the school.
So, I was basically told that the choir was full, and they were not accepting any more auditions, but she could try again next term. As I came out, another mum said to me that her DD wanted to join the choir. I told her that I had just been told that the choir was full, but perhaps she should ask anyway. Well, the next day, her DD auditioned and was allowed to join the choir. My DD was even more upset after hearing that.
I do think that at that age, all the children should be allowed to join the choir, no matter what their ability is. If they don't turn up for practise or mess around, then they should have to leave the choir.
I don't think you are being pfb, OP, I think that in primary school, all children who want to take part should be encouraged.