On what basis can you state that AI techniques are not actually used at this feature ?
By the way, AI is a generic term used for a knowledge field, having numerous algorithms that achieve such functionality, and even the most powerful one may have not a better performance when compared with the human mind; the machine is only faster, not smarter. It is precisely in the most critical cases, where human intelligence can finalize a layout, seeing alternative routes, or even deliberately "violating" certain rules or repositioning components during routing time ( something the auto-router would not do).
In general, for the auto-router works effectively, it must be properly configured in respect to the rule's parameters .