>Citadel and Two Sigma both have had large teams working on this for years. They are making a lot of money doing it but barriers to entry are very high. You need to collect all the data in a way such that you can reconstruct how it looked at any point in time. The vendors can’t be trusted to not make retroactive corrections, so you have to collect it for years before it becomes useful. Doing that takes a lot of time and money.

As someone who works in this space I assure you the barriers to entry are not that high. If I were to sort the various lists of accounts alphabetically you'd see names like Citadel and Two Sigma flanked by hoards of tiny funds you've never heard of. Many of these funds you've never heard of are 5-10man businesses or teams within larger funds. Making money is much more of an algorithms problem than a resources problem.