In fact they changed their pricing structures a few years back to generate more of it.
In the olden days (about three years ago) they used to charge brokers for each trade executed on the ASX. Now they charge a % of the aggregate daily turnover.
This has allowed brokers to split up large order into tiny parcels. Previously brokers would find it too expensive as they would have to pay for each trade executed.
The main reason why bot trading exists is to limit market impact (buy/sell stock without dramatically affecting the price) and allow the brokers to achieve or better VWAP.
