Part of my job is something like that. I make custom programs for my department in the university. I don't care how long is the copyright. Anyway, I like to milk the work for a few years. There are some programs I made 5 or 10 years ago that we are still using and saving time of my coworkers and I like to use that leverage to get more freedom with my time. (How many 20% projects can I have?) Anyway, most of them need some updating because the requirements change of the environment changes, so it's not zero work on them.
There are very few projects that have a long term value. Games sell a lot of copies in a short time. MS Office gets an update every other year (Hello Clippy! Bye Clippy!) , and the online version is eating them. I think it's very hard to think programs that will have a lot of value in 50 years, but I'm still running some code in Classic VB6.