I'm not defending this but there was (or has been) enough political motivation and intentionality in GNU/Linux systems to make binary compatibility a hassle. People actually made decisions against backwards compatible APIs, intending to cause issues and forcing open-sourcing.

Binary compatibility means closed source has a chance to grow in an ecosystem. It requires "responsible" developers to put more effort into designing APIs and keeping them alive. It adds complexity that requires a more stable set of long-term developers; in contrast, the constant churn in FOSS requires lower barriers for contributions. With stable APIs/ABIs you have to live with decade-long mistakes. You cannot "just fix it" in a next major bump.