Tours can vary based on contracts they negotiate with the cruise lines. A zipline is more limiting as to capacity so it is possible Royal Caribbean didn't want to deal with reduced slots for the more comprehensive tour. It can also be a problem with the port times. Some ships will be there at different times of the day, or for different lengths of time. This can cause the tours being offered to vary.
If you wander off the set schedule for a ship's tour you are on your own, and would be responsible for finding your own way back to the ship. All you can really do is ask your questions about the tour and transportation HERE
at the tour operator's website.