Some of the negative nominal premium comes from the fact that you need these govt. securities for collateral, REPOs, clearinghouse margin, etc.
That doesn’t explain *the change*, but this point is often overlooked and it makes the puzzle somewhat less mysterious.
In part, negative nominal (and real) rates reflect a scarcity of good opportunities *at the margin*, but of course inframarginal opportunities may be fine.
If you wish to try a further de-weirding of this, it may reflect a truth about agency problems rather than absolute pessimism.
If capital is relatively plentiful, and talent is super-scarce, and you don’t know how to find marginal talent, you may be stuck just storing your money. But when talent and liquidity are combined — say Mark Zuckerberg — it will earn phenomenal returns, the other side of the coin.
In other words, this may all be a kind of correlate to income inequality and massive returns for founders…
…you have extra money, you really would like to lend it out for a real productive investment, rather than storing it at slightly negative nominal interest. [savings glut, a’la Softbank]
But whom to trust? Who is your local Mark Zuckerberg? You just don’t know. The uncle you might give it to will just rip you off and he is a dope anyway. [tech talent harder to spot because you can’t rely on traditional credentials]
If the agency wedge is larger, because the talented are already occupied for the most part, you might just have to store it.
This implies mega-returns for good talent spotters, which in fact we observe as of late.