Eyes is a so-called “background theme”, this means it basicyally consists of a background (which is enough for image maps) but it does not have enough files to create random maps, most importantly, it lacks the land texture.

Technically all themes which do not have a icon.png or icon@2x.png file present are not displayed in the menu. You could manually fix this by adding these files to that theme. But keep in mind you can only use this theme for image maps. For random maps or image maps without a map.png it won’t work.

You can learn more about the files used by themes here:
https://code.google.com/p/hedgewars/wiki/ThemeFiles

However, in my opinion it would make sense to make certain background themes available for image maps, because they do not need a land texture.

I have created an issue here: https://code.google.com/p/hedgewars/issues/detail?id=842

Image maps without a map.png do need texturing and decoration.

In addition, not all disabled maps consist of only a background. They may simply be low quality. Cake fell in that category before Randi started improving it.