This is definitely a YOU problem.
Why aren't you in assembly?
I don't celebrate.. Eid, Xmas, Passover..whatever the assembly is
Why aren't you in R.E.?
I am
Why aren't you coming to the school disco?
if it not a religious disco, you'll see me there
Why aren't you in the school production?
if its nativity...becasue i dont celebrate xmas...if its Annie, i'll be Rover the dog
Why aren't you joining the netball team?
coz I'm in football, gymnastics, swimming and drama club...insert club/team of choice
Why aren't you coming to Julie's birthday?
Don't celebrate bdays, but I hope she has a lovely time. I hope Julie can make it to my end of SATS party so we can still have fun another time
Why aren't you making Christmas cards?
I don't celebrate Xmas, but pass the Prit stick.. I'm making a Minecraft Snowman card
Why aren't you doing the nativity with us?
I don't celebrate Xmas
Why aren't you dressed up for St David's, St Patrick's Day?
I don't celebrate saint days
I mean these questions are tedious but I was embarrassed by them i had other stuff going on as do my kids. Anything outside of religious PARTICIPATION is the choice of whoever raised you.