keesha said:
For a great many people professional tradesmen exist as a high-priced option to do work when the DIYer can't do it. In rural areas with minimal building inspections people frame small barns and additions and things on their own. A lot of people do their own trim carpentry and drywall, and it doesn't matter if it doesn't look good as long as they're happy. A lot of DIYs understand on a basic circuit level how a home electrical system works. Mention a trip curve, bundling, or even burial rated cable and you get a blank look. Still, they can install a "working" system where the receptacle powers the vacuum and the switch controls the light the way they want it to. They're short sighted to the point that after they live in the house for a while and their lacking knowledge causes problems, they don't blame it on themselves and their incorrect installation practices. They don't know the difference between the light switch working and an installation that will be safe and maintainable and work for years.
With plumbing it's different. On supply lines it's quite obvious if you messed up when you see water coming out. DWV (drain-waste-vent) lines are a little more complicated with venting techniques and proper slope, but basically if the drains go down and the pipe doesn't leak you're OK. I'm friends with plumbers and pipefitters and I'm not trying to dumb it down, this is just what the homeowner sees.
Maybe it's like this - on residential electrical, 25% of the knowledge is getting it to work right initially, 75% is making it work safely and correctly for many years. On plumbing it might be the opposite. Incorrect venting on drain lines will show up immediately if hubby screws it up, it doesn't develop over time like many electrical problems. Makeup of joints is the same way. A poor wire termination on a backstab, screw terminal, or wirenut will probably work for a while, but a poor sweat connection on copper starts leaking immediately.
To summarize, plumbing is an area where it becomes obvious very quickly to a HO/DIY that they don't know what they're doing. On electrical work evidence that they screwed up takes long enough to appear that they don't connect it with their incompetence. Maybe this is off base, but it's from observations growing up around a lot of people that did almost all of their own work on their homes. Some of them learned from their mistakes and got better, some just live in messed up houses.