The key difference is that bonds are financial instruments that serve different purposes than direct ownership. They're designed for institutional investors who need regulatory compliance, can't directly hold crypto assets, or want exposure without custody responsibilities.
Bitcoin bonds also offer predictable returns through interest payments, unlike Bitcoin's volatility. For conservative investors or institutions with strict investment mandates, this structured approach makes sense.
That said, you're right that for individual investors comfortable with crypto exchanges, direct purchase is often simpler and more cost-effective.
Different financial tools serve different market segments - what seems nonsensical for one investor might be perfect for another.