It's just that experiments in astroparticle physics are expensive and have lots of people on them. Like, how is the IceCube Collaboration supposed to write an anonymous paper? Even the most cursory description of the detector would give it away...
Well, maybe there will be many IceCube's later? (Probably not, but I'm routinely shocked when I learn about new giant testbeds in my field...)
Alternatively, when IceCube 2 comes out, the old IceCube crowd might be focusing on other stuff, and not paying attention to the IceCube 2 politics. That makes them great peer reviewers (no horse in the race, but knowledgeable).
The proposed IceCube Gen2 is mostly a superset and only slightly disjoint with IceCube (for example, I am not an IceCube collaborator but I am on Gen2...). But the point is that for experiments that are larger than a few PI's, anonymity of authors is basically impossible (since all papers have everyone on them).
