One of the important requirements for a patentable invention is that it must be "useful".
This patent originally covered a way to provide compatibility between short and long file names. But nobody has used short file names in decades.
So now, the "feature" continues to be necessary only so that FAT can provide compatibility with itself. That's like begging the question. The feature no longer has any intrinsic usefulness, and in fact just serves to make the file system format more convoluted and less efficient.
The patent system ought to be changed so that any patent should be revoked once it is no longer useful for its intended purpose. This particular patent has recently been "useful" solely as a way to give Microsoft leverage in the media device market. The covered feature provides zero benefit to end users.