• Everything is in one library which offers consistency for all operations.
• You can use forward slashes on Windows paths, which makes for much better readability.
• You can access all the parts of a pathlib object with attributes like .stem, .suffix or .parent.
• You can easily find the differences between paths with .relative_to()
• You can easily build up complex paths with the / operator (no string additions).

Just off the top of my head.