Everyone in the collaboration is an author. This is typical for particle physics collaborations. Not everyone contributed directly to this analysis of course, though everyone's feedback was solicited. Some people contributed to construction, instrument design, deployment, calibration, operations, monitoring, maintenance, common data processing tools, etc. the acknowledgements list the people who did most of the work but even they were advised by a larger group of people (I was one of them :) ).

Note that the author order is alphabetical but one of the primary authors happens to be first alphabetically.