Why is it so hard to say for sure? Here’s a nice article in the CERN Bulletin that lays out some of the difficulties.
Due to the huge amount of inter-dependency between different areas of work in the LHC, even a small change can necessitate a complete overhaul of the schedule. For example, something as simple as cleaning a water cooling tower – required regularly by Swiss law to prevent Legionella – has a huge impact on the planning: “When you clean the water tanks it means we don’t have water-cooling for the compressors, that means we can’t run the cryogenics, so the temperature starts to go up,” explains Myers. “If a sector gets above 100 K, then the expansion effects of heating can cause problems, and we could have to replace parts.”
That may be cold comfort (get it? cold comfort!), but it’s the real world. I have no strong opinions about the job CERN is doing, except to recognize that this is the most complicated machine ever built, so patience is probably called for. The particles and interactions are going to be the same next year as they were last year. (Or if they’re not, that would be even more interesting.)