The reason it's like that is that many don't have very good setups for keeping track of all the stuff that has been changed unless it's new features. The other reason is that someone needs to translate the issues to a layman version of what the fix is because the internal terms used won't make sense for anybody but programmers.It blows me away that software updates saying "bugfixes and general performance improvements."
If I was a software engineer on this stuff I'd be furious. Oh that project I've been slaving away on? Management considered it, officially
"Computer stuff or whatever."
No way consumers, or other companies would want to know what got fixed, why it happened, or how they fixed it.
So it's just easier to write "bug fixes and improvements", especially when most users won't care about what the exact fixes are unless they are affected by the issue. I would like more detailed lists of fixes too but unfortunately that's not the reality.