There are many opportunities for institutional investors to trade in exactly the manner you suggest. NASDAQ runs the opening and closing cross as well as other

There are many opportunities for institutional investors to trade in exactly the manner you suggest. NASDAQ runs the opening and closing cross as well as other intra-day crosses. Other platforms allow private crosses, dark pools allow crossing not in public and today 1/3 of all shares are crossed internally on brokerage platforms. Institutional investors have many opportunities to trade in the dark. There is a price to be paid for instantly accessing liquidity in the market, and it is much cheaper than it used to be.