Well, that would be why. As that article points out, files you upload can’t be more than 10 megabytes in size.
The optimal solution is to unzip the files on your own computer, and upload them via FTP directly (assuming none of the individual uncompressed files are over the size limit on their own).
Do you think you could show us one of the files that won’t upload? My guess is it may be over the limit, or otherwise be restricted from being uploaded.