Is it perhaps possible that some might opine that the historical context of an idea is worth knowing as part of reading the end of the book? It just might be worth considering that the historical implementations of policy around usury could not be divorced from the abstract reasoning.
In a way, it's like discussing historical Communism and Communist thought while pretending Stalin, Lenin, and Mao never existed. They all form part of the historical context that really needs to be considered an integral part of the whole.
Again, you're completely correct. There's a great deal to be learned from history!