The campaign around Nemesis was kind of forced by the construction site being so unavoidably visible to the public. You can see it from the monorail plus they wanted to keep Galactica open so guests have had to walk by the construction site every day. At least having the marketing campaign explained the ride closure/demolition a bit for the general public (especially during the phase when most of the track was removed) and helped prevent rumours that Alton Towers was removing yet another ride without replacing it with anything. They probably figured that the marketing costs were worth it to try and build a bit of hype and recoup some of the costs around rebuilding what is essentially still going to be a 30 year old ride design.
For Project Horizon I can definitely see them playing the secrecy angle until the closed season a few months before it opens. Probably something like Curse at Alton Manor or Th13rteen levels of marketing (except they will actually set correct expectations for type of ride experience). I imagine that they will want to deter the theme park vloggers from being too close to the site during the major construction work phase as there is going to be a lot more going on (site clearance, groundworks, utilities, heavy equipment, cranes, building a huge steel building etc) whereas the works on Nemesis are smaller and more localised (e.g. they didn't have to dig out the pit again). And besides, the theme park vloggers create free marketing for Alton Towers by speculating on absolutely nothing with clickbait titles (already happening even though no work has started). It is easier to close that part of the park off to access but we will still probably get spoilers well before the marketing campaign starts. There will definitely be drone shots at some point (I remember the good old days when bloggers used to pay for general aviation flights to get aerial shots of The Smiler construction).
