If you studied the history of finance. Financial instruments are invented adhoc. They are not made or created as part of a grand design.
For example the theory on how banking came about or how we use paper cash to represent wealth was literally an organic concept that slowly came to be over time. People needed to store grain, so someone formed a grain storage business that gave out paper certificates as proof of storage... people started trading those certificates as if it was cash... the storage business owner realized he could just print out those certificates and loan it out... hence the creation of banking and loaning...
That's the basic idea behind how banking formed organically. It is complex not by design but by evolution.
If you studied machine learning and genetic algorithms you'll know that natural selection and random walk does not always lead to the most optimal minimum and your walk will spend a lot of time wandering the entire space of possibilities before converging on a possible sub optimal solution. Finance is such a walk. Random designs eliminated by natural selection. We are more than likely in the middle of this random walk heading towards a solution that like all of our software is more than likely a sub optimal minimum.
Nobody needs to understand finance completely to know this. They just need an understanding of the properties of the real world in general. Finance IS overly complex you and I don't need to be experts in finance to know this.