They are a record of the process of adding to the Linux kernel. Such background can be used to trace the history of contributions if those contributions turn out to have had malicious intent or were derived from code that came from sources that were not compatible with the GNU license that the kernel is released under.

It is not recursive though. A directory is a special kind of inode that enumerates file inode numbers and when that list changes then the contents of that “directory inode” change. But if /home/user/.bashrc is deleted then the timestamp for /home will not be affected because the timestamps are associated with inodes rather than directory entries (assuming no symbolic links are involved).

https://www.redhat.com/en/blog/inodes-linux-filesystem https://en.wikipedia.org/wiki/inode