The underlying reason for the trial was that the event came close to being a "worst ever transport disaster" (full 747 impacting a full hotel, wreckage path would have taken out the airport rescue, firefighting, emergency communications and police facilities and hit the the access routes to the airport which were full of rush hour traffic etc.) Normally the UK AIB would have investigated it but they were fully occupied with dealing with the PanAm Lockerbie bombing plus British Midland. Kegworth crash, so since there were no injuries and no damage it was left to a internal investigation.
Powers that be in the CAA felt (quite rightly IMHO) that this was severely flawed and resulted in little effective action to prevent repetition. They then pursued the prosecution route which in itself only succeeded in proving what an inadequate tool criminal prosecutions are for investigating complex matters like this.
(See event 3 on this link which also links to a substantial article on the event)
Appendix: Internal culture and resistance to change. | PicMA
Also well covered in Matthew Syed's book "Black box thinking".