It is quite different to cut prescription paracetamol (the cheapest chemist unbranded version -exactly the same items as branded expensive ones-
costs about 60p for 32 tablets ) compared to cutting GF prescription items.
Paracetamol will always needed to be bought by many consumers but GF foods are only really necessary for coeliacs.
We coeliacs are not many compared to the many 'faddist GF' people who have chosen to buy GF items in large enough quantities for supermarkets to make a profit from GF foods.
I guess some few Gf items might still be stocked in health food shops (as they were before the GF diet craze).
However, prescription-only GF foods will not be available there anyway and GF items off scrip will always be expensive compared to the gluten versions.