Probably for copyright and license. It's a common feature, MS Office documents include even more metadata, such as how many times the file has been saved.
My problem isn't with quantity of metadata. It's with personally-identifying data. And I can't imagine what the filepath could ever have to do with copyright or license.
Inkscape probably treats the source SVG differently than an optimized output SVG and includes additional data to make editing the file better. Other apps use a proprietary format for their source files that contains this additional information and have to export to an open format for output.
