Decorations, staffing, changing, emergency services, traffic control, maybe the area just isn't great to look at right now. There could be quite the multitude of reasons.
Yea they've used that area in the past for staging of ride delivery, but some things here:
~Doesn't make sense to get the parts when the construction, environmental impact, planning, and any other permits haven't even been filed yet.
~They haven't even started clearing out vegetation. Doesn't make sense to take on parts that need staging when you haven't even started that.
~Just because a fence wasn't used one time doesn't mean they don't use it the next.
I've been around parks enough to be familiar with this stuff. Sometimes they put up a fence, sometimes they don't, sometimes they stage stuff there, sometimes they put it up because they like the looks. A fence is a fence and nothing more.