It has nothing to do with engineers "adding some reality". Designs for complex buildings like museums go through dozens of iterations before they are built, and as the design is refined things change, often in response value engineering pressures.
When renders for a project that's still in its early phases of design are published what you see is the architects attempt to hide the fact that like 80% of the building still hasn't been designed. That's just how it works. It's their job to present the idea of a building in such a way that makes it look realistic and feasible, even though months of work remains to actually make it buildable. If they didn't do that then nothing would ever get built because we wouldnt know what it's going to look like until shovels are in the ground. That doesn't mean they don't know how to make it work and that they need an engineer to come in and save them