because it has less ram than actual minecraft, as well as being tricky to deal with since my computer doesn't open the files the same way as i open the minecraft file/.jar, making things like texture packs a bitch and a half. that coupled with the fact that i can't go in and play with settings, spawn rates ect is really annoying when i feel the need to reduce the spawn rate of the one annoying mob that every mod with mobs has.