I think we are all talking about the same desk, namely the galant. I mentioned recently that I work with a dual monitor setup and the second monitor is on a monitor stand. The monitor stand itself is stable and rests on rubber buffers, but due to the elevation, the wobbling is disproportionately amplified.
The actual cause of the instability lies in the desk's structural mechanics (thanks to my engineering studies) because the construction of the desk is, as the expert says, "statically indeterminate." As long as the frame corners of a rectangular structure are not connected by at least one cross brace (like in a truss house), the entire construction remains unstable. You have to imagine it like a rectangle that turns into a parallelogram under load. There are desks with a wide connection between the legs that solve this problem, but those cost quite a bit more.