As most of you probably know, institutions use a variety of dark books, crossing networks, hidden liquidity pools etc to move large blocks of shares. I assume this is to not impact the market price of the given stock, and to obtain a better/faster fill. As many of you also know, hundreds of traders have made it their entire strategy to arb these gateways, and are doing it with incredible success. You've probably seen the Pipeline commercials claiming leak proof block trading, but i've seen and personally done arb on those orders, so their claim is BS. What im wondering, is why such networks/dark books even exist? Is 3, 5, 10, 20 million dollars a month just such a small amount that it doesnt matter that these traders are scalping the crap out of them? Certain gateways are worse than others of course, but overall i just dont get it. Does it cost more to employ someone to fill you 50k shares of BNI, than to send a 50k buy order to a dark book algorithm and have 20 traders scalp you for 25,000 bucks? Please help me add context to this.