AAIB will tell us the answers.
I would not be so sure the AAIB will provide all the answers in terms of cloud layers, VMC v IMC, in / out of cloud / fog, what he could see of building and/or crane, or even where he was v where he thought he was.
Firstly, they will not have all the data required. They will have numerous eyewitness reports (from Ground level), and probably GPS data over and above the radar data published. Also CCTV from largely ground level. How these can be used to construct the "view" from the cockpit must be limited?
But mainly because their remit is not to diagnose
exactly what happened. Their aim is to prevent a recurrence. If basically the (S)VFR rules were clearly not being followed, either as a one-off or industry "practice", or the Heli-Lane rules v Wx minima v 500' rule etc. left loopholes then they will make recommendations to close / clear them up.
Furthermore, and very "IMHO", the AAIB tread carefully in stating "what" happened without strong evidence. They (again IMHO) do not want to feed the lawsuits more than necessary, especially where this strays outside the main aim (see above).