I agree that this is another factor, and I'd like to get into some nuance of it...

If we go back to the RMS school of code sharing, which influenced much of contemporary open source, they're very big on licensing to control how the code is shared.

This was actually a break from some of the earlier thinking by some programmers (not all), that code is implicitly public domain, or should be. RMS said, yes, sharing is good, but we need rules to keep the sharing happening.

Once "open source" was coined (by ESR, et al.) they were also big on licensing, including RMS's licenses, but most of the reasons were more about commercial needs.

Since then, people participate in open source for a variety of reasons, many of them commercial-adjacent.

But I suspect most people don't think much about the hard-earned licenses that helped create the current environment, in which this wealth of loose sharing and collaborating is happening.

We're only starting to see the effects when some AI companies ignore the long tradition of licenses that built open source.

Writers and illustrators, on the other hand, as you say, don't have that tradition and institution. (There's also things like the sometimes tolerated gray area of fanfic using others' characters and situations, but AFAIK not official and organized like open source.)

And so maybe the essence of what's happening is more readily obvious to writers and illustrators, than it is to programmers.