The primary innovation of bond ETFs was democratizing access to the bond market, which was previously a non-transparent, "voice-driven" system with uneven access. ETFs provided a portfolio of bonds with real-time, on-exchange pricing for all investors, fundamentally changing market structure.

Contrary to fears, bond ETFs proved their resilience and liquidity during the 2020 pandemic crash and the 2022 rate shock. These events served as critical tests, cementing investor confidence and triggering a new wave of adoption when underlying assets were hard to trade.

The rise of electronic and portfolio trading has made public credit markets as liquid as equity markets. This 'equitification' has compressed spreads by eliminating the historical illiquidity premium, forcing investors into private markets like private credit to find comparable yield.

For 99% of ETFs, liquidity and bid-ask spreads are not based on the ETF's own trading activity. Instead, they reflect the cost for a market maker to buy or sell the underlying basket of securities. An ETF holding liquid stocks can trade billions with tight spreads, even if the ETF itself is rarely traded.

The presence of a large, actively traded ETF forces the development of automated pricing and trading infrastructure for the underlying assets. This is why CLOs are electronifying faster than other, similarly complex securitized products that lack a major ETF.

Today’s private markets are undergoing a fundamental market structure change, much like public equities did with decimalization and ETFs. This suggests the current illiquidity and complexity are features of a maturing market, not just a temporary downturn.

Many investors mistakenly believed private credit funds offered semi-liquidity, not understanding the underlying assets are fundamentally illiquid. The realization that liquidity is a discretionary feature, not a guarantee, is causing a healthy but painful exodus from the asset class as mismatched expectations are corrected.

A key advantage of using defined-maturity bond ETFs is immense diversification. A single ETF representing one 'rung' of a ladder can hold hundreds of individual bonds, a level of risk mitigation that is practically impossible for most investors to achieve when buying individual bonds, especially with limited capital.

The rise of systematic and electronic trading has fundamentally altered credit market structure. Turnover for every dollar of bonds issued has doubled from 3.5x to 7x in a decade, creating a deeper, more resilient pool of liquidity that is less prone to disappearing in a shock.