many home owners want everything cheap as humanly possible, so they find people willing to do it for below minimum wage (immigrants)
For the record, many home builders also think this way. Unfortunately, most home buyers and owners don't have any sense of what qualifies as quality materials or labor.
This is more the problem. Just because you're paying more money doesn't mean your buying quality anything - someone may just be pocketing the difference.
The general practice I've seen is that the builder has a couple of low-wage teams to come in and throw it together. And then 1 or 2 guys who come behind them and fix their screw-ups, if the homeowner even notices.
For the record, many home builders also think this way. Unfortunately, most home buyers and owners don't have any sense of what qualifies as quality materials or labor.