It's because it's a unix text file, not a MS-DOS type text file. In unix, each line is terminated with a single character, a line-feed (0x0A). In MS-DOS/Windows, each line of a text file is terminated by a pair of characters, a carriage-return (0x0D) and a line-feed (0x0A). The reason your file appears on one line is because you need to add the carriage-return to each line.
In Sun Solaris, there are two utilities called dos2unix and unix2dos that do this conversion. You would just need to run unix2dos on your file before uuencoding it.
If you are using a different flavor of unix, you'll need to find the equivalent utility, or write your own.
Also, I believe if you view the file in WordPad, it will look ok. WordPad goes ahead and wraps the lines.
Hope this helps.