The most charitable interpretation of that quote is that after RegNMS, multiple trading venues became legalized. Liquidity providers then chose to spread liquid

The most charitable interpretation of that quote is that after RegNMS, multiple trading venues became legalized. Liquidity providers then chose to spread liquidity out because it was now legal. Here is RegNMS. Find me a place where it says liquidity must be divided between all possible exchanges: https://www.sec.gov/rules/final/34-51808.pdf https://www.sec.gov/rules/final/34-51808.pdf