The following quote is from Hayley McDowell, “How to Deal with a Billion-Dollar Credit Portfolio Trade,” The Trade, October 30, 2019 (https://www.thetradenews.com/deal-billion-dollar-credit-portfoliotrade/) concerning bond exchange-traded funds: “Bond ETFs … have played a crucial role in the evolution of portfolio trading in credit, and particularly for the electronification of credit trading in investment and high-yield bonds.” Explain why.