Almost no-one has "secret painting methods", or "secret plumbing methods".
For plumbing, building codes dictate the range of solutions that are available for any given problem, and they're not secret (but buying a guide can be expensive.) However, painters, plumbers, and other trades definitely have tips and techniques that they've learned through experience and from mentors, and you won't find much of that being given away freely. You've got to learn it the way they did, through hard work and apprenticeship. And that's ok, because those skills require mastery to use properly, and that's true in software development too.
> However, painters, plumbers, and other trades definitely have tips and techniques that they've learned through experience and from mentors, and you won't find much of that being given away freely.
Exactly this. My father is a civil engineer who's now in his early 60s, and he recently got to work with colleagues much younger than him.
He told me that said colleagues didn't know some trade-related stuff which hadn't got covered in university courses (like how to reinforce earth ditches when digging in mountainous terrain with probable heavy rains) but which was paramount in keeping the work going (not much that you can do once a ditch collapses because of heavy rain). He told me that in this instance he had instructed his younger colleagues on what was the correct procedure to take, but he also told me that he's got other professional secrets that he's not ready to share just yet.
For job security, I think. We're lucky enough as programmers not to have to worry about that too much, but when you're a civil engineer in a quite poor part of the country and the continent (I'm talking Eastern Europe) you do not have much better other options.
Speaking as an artist, this was untrue for us as well pretty much until the internet democratized things. Prior to this the assumption was that if you're good you should just be able to do it or that it should locked up in guru-like ateliers that parcel it out at high cost like Scientology courses. Of course access to basic art instruction has always been available, but a lot of advanced techniques or knowledge in specific subdomains (e.g. animation) was pretty closely guarded.
Those professions cannot be compared with software, you would have to compare an industry where the product is intangible.
Do you see musicians making samples and giving them away to other musicians for free? Sure, you can find some online but it is definitely not the norm.
Does Hollywood create stock footage and release it for other production companies to use for free?
Do photographers allow others to use their photos for free?
I reckon the increasing popularity of FOSS is paving the way for the examples you've listed to start becoming mainstream. Social media is already starting to kick that third one into gear, and I wouldn't be surprised if the growing remix culture soon evolves into licensing terms that expand fair use to "you can sample my song as part of your song as long as your song is substantially different from my song".
I've been in AEC since 1989. I can count with the fingers on one head the number of times I've seen individual architects form a community based on unpaid contributions to some big firm's profit driven project. That's bread and butter at Google.
The difference is that construction has long been a commodity industry and software has not become one yet.
I can go to planning offices and see the plans of any building. Almost no-one has "secret painting methods", or "secret plumbing methods".