I don't think this is due to illegal aliens, without which our construction industry would be in even worse shape, but rather that there have been massive declines in the competence of domestic workers across the board, and this has been hidden by outsourcing, importing skilled workers, and technological growth (e.g. have machines do things that domestic workers cannot), so that you see productivity declines in those areas where you cannot outsource and you cannot pay extreme wage premiums to attract people with basic reasoning skills.

You can see this literally everywhere. Unless you are going to pay 200K+ you will have difficulties hiring reasonably intelligent, motivated, conscientious workers.