The main issue is the auto-router has no idea what any of the components are or what their requirements are. It just knows roughly physical dimensions and it's connected nets (traces between pins). These component requirements aren't something that can easily be "programmed" into the tool either - every component has it's own requirements, and they're not just electrical (such as needing certain amount of space around a component, or not placing next to other types of components, etc).

Without that knowledge, it's impossible to create a good auto-router/layout tool. The tools often just stack components as close together as physically allowed by the necessary traces.

For very trivial stuff, it might work ok. Anything else, no chance unfortunately.