It's not about buying a return, it's about buying stability. If you've got a billion dollars/euros to manage, and assuming you can't just stuff notes in a matt

It's not about buying a return, it's about buying stability. If you've got a billion dollars/euros to manage, and assuming you can't just stuff notes in a mattress and hope silverfish don't eat them, you also can't just dump it in consumer-grade investments (typical bank insurance wouldn't cover most of it if the bank collapsed). Virtually any combination of stock/bond/tangible/land market investments, no matter how diverse, has non-trivial risk of significant loss over some time horizon. In contrast, the most premier government bonds (US, German, maybe Japanese and/or Canadian) have a huge "too big to fail" factor. If those suddenly lose 30% of their value, it probably means the world a a whole has far bigger problems than your investment portfolio. If your goal is asset preservation above all else, it's worth eating a known, predictable zero or negative rates of return on those bonds, as a safe harbor from the much bigger risks of the broader market.