[elecengin]

This fits with the general trend in trading in fixed income markets versus equities markets.

Due to to the lower amount of liquidity (inventory available for someone who wants to buy/sell), fixed income (bond) markets tended to be traded traditionally - by negotiating with a number of firms individually (whether electronically or over the phone). These traders are extremely worried about someone hearing about their order and trading ahead of them (the actual "front-running" that Flash Boys accused HFTs of doing!) Therefore, they want to carefully release information about their interest in buying/selling to brokers they can trust.

These markets are stubbornly difficult to automate. Attempts at creating open markets where participants can trade anonymously with other participants have mostly failed except in the most liquid fixed income markets. Even though treasuries are some of the most liquid bonds "on the run" (recently issued), other maturities can be extremely illiquid.

[HiLo]

Most commodities markets get really thin a few years out the curve as well, so if you're a large producer wanting to hedge your production the next few years it may still be pretty tough without lots of slippage.