Cows and others,
Perhaps as the aircraft removal took a few days as did the search for casualties....the AAIB was delayed in doing their preliminary investigation.....thus the first Preliminary Report will take a bit longer than normal.
If the wreckage had been in an open field, there had been some radio transmissions indicating the general nature of the problem, or a CVR or other recording device retrievable that would have shed some light on the situation....the Preliminary Report would be done already.
None of that was the case here.
The absence of any other communication....AD, SB, etc....is no indication of the status of the AAIB Investigation or their state of mind as to what caused the Crash.
The mere fact the aircraft was inside a Structure thus complicating the rescue/recovery efforts by Emergency Services work is significant both in delay but also that it added "damage" to the aircraft that has to be accounted for along with figuring out what was actual crash damage and quite possibly what was damage incurred prior to contact with the Structure.
This is going to be a very difficult investigation for many reasons.
it will take time....possibly quite some time.