I think one problem is thinking of the trades as a place where you put people not (good|competent|intelligent) enough to go through college. (Some people's conception of the armed forces makes the same mistake.)
Go a generation or two back and in the UK, we had a much clearer separation between working and middle class, for example one got paid weekly or hourly wages, the other got paid a monthly salary. The trades themselves were divided into skilled and unskilled. While it made a huge cultural difference which class you were from, a good skilled trade could easily make you more money than a clerk job. (Bob Cratchit was middle class!) An unskilled day labourer such as a stevedore might live from hand to mouth, an engine mechanic could usually afford to raise a family and afford a place to live (in a working-class area).