The link between corporate bond credit spreads and secondary market illiquidity in the cross section has grown stronger since 2005, resulting in a higher liquidity component in credit spreads. Using U.S. investor holdings data, we show that short‐term investors (e.g., mutual funds/exchange‐traded funds [ETFs]) increase trading activities in the secondary market, amplifying the effect of secondary market frictions on prices. We provide a model featuring heterogeneous investors with different trading needs and heterogeneous bonds to investigate the impact of the rapid‐growing mutual fund/ETF sector on the corporate bond market. We find the change in investor composition can quantitatively explain the aggregate trend.