I create trainers because that's what I'm good at. I don't know VB, C++, or any other high level programming language, but I am halfway decent with LUA and Cheat Engine.
And trainers are far from being the only hacks available. Just because that's mostly what you see released on here doesn't mean that's all there is. I use my own personal hacks that increase your loadout capacity beyond 10 items and allow you to have other things such as 5 semtex at once. But have I posted it on here? No, because if it's made public then everyone will be using it and Treyarch will know what to look for and the ban hammer will start swinging.