Linus is also kind of obsessive about this at the kernel level. I wish more of the userland shared that priority (cough cough)
Yeah, the driver ABI in Linux is totally stable. Cgroups as well!
A big part of it is the ecosystem is mostly/almost entirely open-source, so in theory you can update all your applications to use the new API. So breaking changes are not as big a deal in that world, as they are on Windows where you definitely do not have that option due do the primacy of closed-source software. I think this view is short-sighted, though. If there are 100 users of a given library, then it takes 100x more effort to update all the applications than for the 1 library developer to avoid making breaking changes.
I have no specific insight into decision-making in open source organizations, but given that the resources they're working with are several orders of magnitude less it's not surprising to me that they sometimes end up having to choose between stability and new functionality. (While I personally prefer projects towards one end of that spectrum, I'm happy that different projects have different values for other people.)