Earlier quoted context omitted.
There are some ML problems where it is fundamentally impossible to use historical data to make accurate forward looking predictions as its not IID. These fields require you very carefully capture data on sub-optimal choices. In the case of trading this means making explicitly bad trading decisions some portion of the time, and teams that have done this at any scale are unlikely to share the data. In the case of tradi…
I don't get it - if you have accurate historical data, how is this different from having access to current real-time data? Why can't you pretend you live 20 years in the past and use the data you have as if it were real-time?
As you go to shorter time scales you get more usable data, but then you also need to deal with other issues such as latencies/jitter, market impact, complex order types, order book queues, etc. It becomes a different game.