If when baking cakes, and especially pastries, you want less gluten formation, why not use something that has even less gluten than cake flour? What would happen if I tried to make a cake or pastry with cornstarch instead of flour?
You still need some gluten, otherwise the cake will crumble. Any recipe that is gluten free has to use a number of different additives to mimic the structure provided by the gluten. If you just replaced the flour with cornstarch, your cake or pastry would not be able to rise (it would lack the internal structure to "inflate") and likely crumble as soon as you tried to move it.