Apollo and Citadel, two prominent firms in active investing, have raised concerns regarding the increasing prevalence of passive investment strategies, which now account for approximately 60% of U.S. equity funds. They indicate that this shift has led to various market risks, including reduced shorting, heightened market volatility, decreased liquidity, and rising price-to-earnings ratios for major stocks, particularly those in the 'Magnificent Seven' category. The firms warn that as passive funds gain prominence, hidden costs may also emerge, potentially impacting overall market stability.