I may have a outdated notion about the trades you mentioned, but I have seen an "apprentice" model a lot. I have seen it with a masonry where the experienced guy was bringing in his nephew and teaching him on the job. A lot of these trades are family owned and have seen taking in people based on someone vouching for the new guy.

Maybe this varies country to country. I have seen this in India and UK atleast.

In UK atleast there are trades like roofing, landscaping, exterior building cleaning, masonry, tree surgeon etc which I have seen them are mostly family based.