Doesn’t happen to the same degree as in plumbing. With front end or back end, yes there are good jobs and bad jobs, but if the data gets to where it’s going and there’s no bit rot, you’re pretty much done. If the data is in the db and not on the paper forms, and you can’t see it decrypted at rest, it’s a good job. With plumbing, there seem to be endless layers of nuance between good or bad, finished or unfinished.

Also, it should take X hours to code a feature of Y size with this many fields or inputs. There are unclearly established timelines for a job and any big deviation from that will get you fired (or not hired again by the same builder). There’s no “due to this plumber’s lack of sobriety with the world, a project that should have taken 2 weeks took 4 and a half months, and the connections on the joints are poor”.

With all due respect, you probably know more about software than plumbing, maybe leading you to simplify a bit. Because the same logic could be applied to plumbing, but any plumber might see more variables, the way you do with software.

That is another distinction. All the example jobs do routine, repeatable things. Everything a programmer does is either novel or trivially replicable. There is no equivalent to "painting a room of certain size", to do that you use a copy of already existing painted room.

It doesn't happen as much in plumbing or painting because these fields have not had rapid change in the last few decades, so common practices have stabilized. Plumbing also has standardized code and inspections which pretty much make sure that everyone is doing the same thing the same way. And still there are differences in quality. Look at what two painters will do to a piece of shitty material like an oil-painted unprimed piece of plywood. One will sand it down to the wood and prime, the other will just slap a coat on top, and you'll have flaking in a few months.