But why would you want to use AI to control planes?

Aviation is one of the few industries where the largest regular (non-capital) expense is something other than labour, namely fuel. Anything that reduces fuel costs even a little is of obvious interest to every airline.

There are still the issues of coordinating flight paths to avoid collisions, and regulation (including international regulation). The former seems like a technical problem amenable to increasingly accurate approximations over time. I don't know about the latter, but I doubt it's as insurmountable as you imply. International air travel has been around longer than ILP solvers, meaning that at some point flight schedules were created by people. Now they're created by ILP solvers, and the regulatory environment successfully adapted to that change.