If an OS update gives me a better allocator, I want every app to take advantage of it. Same idea with other libraries, if I update a library for reading zip files to make it go faster, or to fix a vulnerability, I want every application that uses that library to take advantage of it.

This is a debatable position. Linux distros usually do this, but a lot of modern applications ship with all their dependencies. I'd say the former is more efficient and generally better from a user perspective and the latter is more stable and is generally better from a developer/maintainer perspective. Open source encourages the former, proprietary software encourages the latter.