What we're seeing here is 40 year old code compile and run with minimal effort. Largely because the C language has respected backwards compatibility.
Yes, there were breaking changes along the way, but they were trivial to resolve in hours. And (more interesting) the author believed that to be true and so persevered.
I saw this recently as well. I run a lot of programs on Windows. Many are 32 bit, written in the 90s for Windows 95, or 98. They all still run. Microsoft bends over backwards to keep things compatible.
I also get to write a lot of web API clients. I tell customers that it won't work forever. Web APIs are constantly changing. The service (especially Google) will change something soon to break it.
The people building those APIs are expecting only currently-maintained apps to run. They have no concept (or experience) of 40 or 30 year old code "just running". Crumbs, if you get 5 years out an API client you're doing well.