It certainly looks like it's about money to me.
Been following this for a while related to pictures on Flickr, etc.
Looks like the NT et al have had "the consultants" in and been told that they are sitting on a gold mine with respect to image rights on all their land, buildings, etc and that pots of gold await them if they start getting "the lawyers" in to enforce such rights - hopefully more gold than it costs to get "the consultants" and "the lawyers" in......
No case law as far as I know and I'd like to think that a reasonable judge (/oxymoron alert mode OFF/) would throw any such case out with gusto, but who knows in the crazy world we live in right now.
Given the overall non-commercial aims of NT etc one can only hope that getting some publicity out there on this will cause them to retract.
I hate to say it but I would guess that TMA will come under their gaze at some point going forwards. I hope not, but I fear the worst....