Files do not have an eternal service life. After the file is worn out it would be too valuable to just throw away. A long time ago old files were reworked to have a new sharp (but slightly thinner) file. This profession however is about to become extinct. As files are usually made from good steel the worn out pieces might as well be turned into knives. Some woodworkers used to grind old files into cutting tools for the lathe.
The texture of the material will not allow for a really sharp edge for most files, however.