If you look at this image cropped from one posted here today:
View attachment 255293
it seems the bridge leading to Slinky has been redesigned from what has appeared in both art and model. Those showed a Tinker Toy creation:
View attachment 255294
There are gaps along the top of the walls that indicate more elements are still to be added (along with paint) but this looks more like Lincoln Logs or blocks to me.
The reason could be location- the bridge passes over the ride track and probably they don't want anyone to be able to drop anything down on to the track or passengers. The design in the concept art had many openings, and this looks quite high and solid. If you look at the approaching worker, you can get a sense of the wall's height.