Second, that so much exists in such massive paintings is because

Does the highlighted section mean "The second reason why that amount of Christian iconography exists in these massive paintings is because"?

Context:

Christian iconography is particularly visible in the paintings commissioned for Canada’s never-built memorial art gallery. There are two reasons for this subject matter. First, religious practice in general revived in the Great War, conveying meanings understood in a Christian context, which could be effectively translated into art. Second, that so much exists in such massive paintings is because the Canadian plan for a memorial art gallery went further than the British one. And it was British artists who received most of the commissions for the large-scale paintings intended for its decoration.