Market makers used to be humans. Now, due to advances in technology, computers can do that job. Computers are (generally) cheaper than humans so they can do the

Market makers used to be humans. Now, due to advances in technology, computers can do that job. Computers are (generally) cheaper than humans so they can do the job for less money. You can see this in the fact that spreads have decreased as market making has been turned over to computers. That's the value they are adding. Market making has always been work so it's always cost money. But now it's cheaper. There's always been money subtracted from the system, but now it's less than it used to be.