Complexity makes systems brittle and exploitable. Also, most of the complexity adds no value. For example, do we still need debt? Wouldn't it be better for a company to just create and sell shares if they wanted to raise funding?
In a healthy economic environment, loaning money doesn't make any sense. When you make a loan, you limit your upside potential but you're still exposed to the full downside risk (e.g. if the debtor goes bankrupt). The only real use case for debt is to create speculative bubbles... You manipulate markets to inflate asset prices so that people need to borrow more money so that the interest payment on the loan taken for that asset is more profitable than any real investment return that the asset could have generated organically.