March 5th, 2007
Crux of the Reason: Unisys and IBM have patented the LZW compression algorithm which is used in generated GIF images. Read the full article.
Also, the page links to a library called libungif, which uncompresses GIF images written using the LZW algorithm and writes them in uncompressed format. The philosophy section of GNU.org is very interesting. Please go through it.