To point out a particular example... One can hire various masons at various prices who would be capable of laying a flat brick or CMU wall. As soon as you require skilled masonry, of real natural stone or in walls or columns with interesting shapes and orientations? Now you're hiring Mexicans or Central Americans. At any price.

One can imagine the several decades of law enforcement that would be required to change this situation, but it is an open question whether it would be a good thing overall.