“Flows are generally not related to expense ratios, and more to do with the market environment in the US,” Matthew Bartoloni, head of SPDR research at State Street Global Advisors, told the Financial Times. “Since March the Trump administration has been more about the art of damage limitation than the art of the deal.”

So far this year, European stocks have outperformed U.S. markets.

Meanwhile, investors with longer time horizons have increasingly focused on the cost of their investments as a way to improve total return. Consequently, the cheaper IVV and VOO may continue to maintain inflows from smaller money mangers and retail investors looking to grow wealth for the long haul.

“Fee differentials are important,” Robert Smith at Sage Advisory, an investment adviser, told the Financial Times. “For us it is a question of what is the least expensive with the highest degree of tracking efficiency.”

Institutional investors, though, put more emphasis on liquidity or the ability to buy and sell a security during periods of extreme stress in the markets, which means that many have utilized SPY over IVV and VOO. Over the past 30 days, SPY’s average daily trading volumes were 20 times those of IVV and 38 times those of VOO.

For more information on asset flows, visit our ETF performance reports category.