High-speed traders have hit the wall. Even as critics of high-frequency firms have argued their speed and technology give them an unfair advantage, the traders are facing diminishing returns. For one thing, there’s been relatively little turbulence in this bull market, a challenge for high-frequency traders and other market makers because it restrains volatility and trading volume, curbing their profits. “It’s not going to come back,” said Richard Johnson, a market structure and technology analyst at Greenwich Associates LLC in Stamford, Connecticut. “For a few years after the crisis, people were in denial and kept ... (full story)