You just reflected a major issue in this. You are applying your belief to fit the narrative. These are real, major, geopolitical and legal promises that are actionable and measurable. They aren't subject to what one believes. They are subject to the real, measurable goal that was promised and is now being backtracked on....
Well, everyone applies his or her beliefs to whatever subject is being discussed.
Trump is not exactly a deep thinker. He's envisioned a lot of huge projects and they have come to pass. Trump Tower and Mar-a-Lago for a couple of examples. I think he thought we could build a real wall.
He also thought that if he were president he could accomplish stuff in the same way the head of a company can. He didn't realize that a president's powers are severely limited by congress and the courts.
So, I don't think this was an empty promise when he made it and I think his supporters wanted a real wall and believed we could have one.
And maybe we can someday ... at least in some places.
I don't think Trump has abandoned the idea of a real wall entirely. I just think reality has sunk it that it will take much longer and be much harder than he thought it would be.