The lender in this case was living somewhere that was likely to flood if the repair works funded by the bond didn't get done, so they might have had some not purely financial motivation for it.
Plus we don't know what other investments Elsken Jorisdochter owned; this was probably a small part of her assets.
Finally, I'm not very convinced by the "400 years at 4% compounding" hypothetical -- could you actually buy an investment with that return at that date which was a safe non-risky one? And if you could, should you as a person with a lifespan much less than 400 years really prefer it over something which gives you a guaranteed income within your life?
Plus we don't know what other investments Elsken Jorisdochter owned; this was probably a small part of her assets.
Finally, I'm not very convinced by the "400 years at 4% compounding" hypothetical -- could you actually buy an investment with that return at that date which was a safe non-risky one? And if you could, should you as a person with a lifespan much less than 400 years really prefer it over something which gives you a guaranteed income within your life?