Answering questions about your past papers; looking over someone else's proposed methodology; or cleaning up an internal tool into one you can share are all great tasks for advancing the field, but none of them bolster a CV, earn grants, or help you get tenure. If you want credit for them, you usually have to commit lots more time to the task, like running a formal discussion, becoming an author, or polishing the tool into an OSS contribution. All too often, the result is siloed projects and work abandoned as soon as it's published. (How many papers offering some novel twist on priming or ego depletion could have been turned into replication-and-extension if past authors had been involved?)
Especially in astronomy, with large projects and lots of non-PhD team members, this makes so much sense. (I believe something similar may happen at LIGO - if not formally then at least in practice?) If work is going to be judged by authorship, it's only fair to recognize that at a certain point the groundwork and floating aid people give is comparably valuable to the act of writing up some chunk of the text.
For people building the telescope (think hardware, software, logistics, everything before the science can be done), many of whom are not academics, and don't typically get authorship or write papers, it's great to get credit for working on the project in a formal, public way. You don't even have to edit or provide some kind of task directly related to the paper either, which I agree can get somewhat clique-ish.