Why isn't there any standard automation testing tools for game development?

There are plenty of testing tools for creating software, a couple come to mind such as Test Complete and Selenium. But I’ve never seen or heard of a automation testing tool designed for the gaming industry, apart from the ones that come equipped with game engines such as Unity and Unreal. But these tools have to be built on, to my understanding they give devs the required code and you build on it to suit your game.

From what I understand automation testing in game development isn't really common, but is still done by some companies, and they do it through different methods such as developing AI that can play the game at a faster rate then a normal player thus discovering the flaws and glitches of the game faster. http://ift.tt/2tFvSSl

But what I don't understand is why doesn't such a system exist. I know that games are vastly different and creating one tool that suits all games may be difficult but certainly not impossible, there is a lot to gain from such a tool.

Is it technical limitations? Or am I simply overthinking it.

I also feel that I should add that I have never used an automation testing tools, neither the ones I mentioned in the very beginning or the ones that come equipped with game engines.