They got the best rate, have more interesting trip stories so far, and overall like their trip has been more enjoyable.
As a tour guide, I meet all kinds of people the ones who booked early usually arrive early with their paperwork already done.
Create a well-rounded plan for each day and leave pockets of time open for adventure. Before you get here the online world will give you a lot of options to build a full itinerary of activities, shows, and entertainment I suggest planning ahead and pre-booking your activities.