No, it's because people who stand to make money off it want it.
Society is full of examples of things that people want and that would save money and make a lot of sense that are blocked by people rent seeking off the status quo. Free tax filing provided by the government is one particularly obvious example.
"Do it better" doesn't work for monopolies. A company offering trades at lower intervals doesn't work when the NYSE etc. controls the actual platform, the minimum fees, the granularity of transactions, etc.
No, it's because people who stand to make money off it want it.
Society is full of examples of things that people want and that would save money and make a lot of sense that are blocked by people rent seeking off the status quo. Free tax filing provided by the government is one particularly obvious example.