GST for Cooperative Housing Society

Why is it so that maintenance amount is different. it shud be uniform for all flat holder's

As per notification 12/2017, in case of housing society, monthly contribution received shall be exempt if the amount is not exceeding ₹7,500 per member.
So, members who are paying above ₹7,500 will be charged GST on the whole amount and members who are paying amount upto ₹7,500 need not be charged GST as it is exempt.