For newcomers, it's not always clear that GnuGo is an AI you can play against, so they would tend to stay away from that button.
If it was labeled differently, with a more common name like "Computer" or "AI opponent", it would be a lot more understandable for everyone. What this computer opponent actually is won't be lost either, because the app tellg you it.s going to prompt you to download GnuGo for that, so the message and the content of this download will still be clear.