There are plenty of cases where it's preferable for those things to be owned and maintained by core teams. One of the biggest benefits of the Linux Kernel is that drivers are distributed and maintained as part of the core kernel. Likewise, one of the biggest disadvantages of not having this model is in software like Jenkins, where recently the creator of Jenkins explicitly called this out as one of their biggest problems. It's not so cut and dry to say what pieces of "added functionality" should be "core" or "not-core".