> The lack of care about API&ABI stability in developer facing open source projects (interpreters, libraries, frameworks, commandline arguments) is still bizarre to me: why make your work hard to use/update?

If you're a FOSS developer with limited time and man power (and if you're lucky, limited budget) maintaining backwards compatibility is hard. So hard, that new features and bug fixes might have to take a back seat to it. Also, I'm almost certain that developers would rather be implementing new features, and fixing bugs, ahead of maintaining backward compatibility. It's much easier to show a new feature or a bug fix, than it is to show how backward compatibility was maintained.

Also, the big users of FOSS, projects like Debian (and Ubuntu) and Fedora, will rebuild their entire systems when new versions of software are released/integrated. This reduces the maintainer's requirements to keep ABI compatible.