Does the app involve circumventing DRM? That could be one reason why the authors are offended....
....either that or they are offended that somebody would want to read their work without the hentai tentacle pedophile who eats babies while painting its house with the blood of their mothers and who only appears for shock value in a story that should have been for young kids....
....why am I thinking about such vulgarity?
edit: Seriously though, the main reason is probably because they are protective of their work and don't want it to be disassembled from drm.