It's nothing to do with speed. In fact, this might slow down the process.
In the past, the process was very unsatisfactory. You made a complaint. The bank answered. You responded. The bank answered. The FSO acted like a postbox.
When all the correspondence finished, the FSO made a decision and that was that. The only appeal was to the High Court.
Now, they issue a preliminary decision. If they have made an error of fact, which they often did, you have an opportunity to correct it.
If they have made a serious error of reasoning, which they often did, you have an opportunity to correct it.
Brendan