The argument is that a system that's trained to be sufficiently good at optimizing some objective in the world must also be get good at optimizing secondary instrumental goals.

I.e. any task comes with the implicit meta task of amassing the resources and the power to do the task in the best possible way.

The point is made very well in the AI drives paper by Omohundro.

I didn't believe that myself at first but I've come around to it. I don't think it's inevitable though, but I think it's quite convincing that this tendency would naturally emerge through reinforcement learning.