To be fair, the situation isn't much better on Windows or Linux. While at least they have a concept of uninstalling an application, you're still reliant on the developer actually getting it right and not missing some tempfile or something.
The filesystem doesn’t have rich enough metadata about temporary files. At least Windows has a file attribute for temporary files (FILE_ATTRIBUTE_TEMPORARY), although I’m uncertain how many apps actually set it on their temporary files; Linux/Unix/etc appears to have no real equivalent. I think ideally temporary files would have rich metadata - the ID of the process, session, and application/package which created them, and some kind of retention policy and expiry date. Of course, one could always use xattrs for that, but unless they are standardised few would use them. C library functions such as mkstemp/mkdtemp/etc could be enhanced to set metadata on temporary files. The OS package manager (apt/rpm/etc) could put an xattr on an executable with the UUID of the package, and then mkstemp could copy that to an xattr of all temporary files. Now if the FS also indexed xattrs, we could upon uninstall find all temp files owned by a given package and remove them.
Many mainframe/minicomputer file systems support file expiry dates, which is an interesting feature which Unix missed.
