Why don't *.ipa files compress well

[dragon499]

On My pc, I navigated to:

C:\Users\Myname\Music\iTunes\iTunes Media\Mobile Applications and found all of my backed up Ipad apps as *.ipa files. For fun, I tried to compress them, using Winzip, Rar, and the Winrk. With the "maximum compression" settings for all of the utilities, I was only able to compress aps on average 1 to 2 % smaller than the original files! I just tested compressing a few windows executable files, which compressed up to 70%.

Why can't I compress the *.ipa files more than 1 to 2%?

 

[Nessaj]

.ipa files have been the compressed ones.
Apparently you can hardly compress a .rar file for a much smaller size.
So are .ipa files.