Nothing "makes" one maintain level flight. OTOH, should one (pilot) decide to maintain level flight then that someone has to follow the laws of nature such as lift equal to weight.
To produce lift in subsonic convergence airflow, one has to provide the airflow with needed pressure variations to attain the needed forces. Given a wing in a 60° bank relative to earth, at I G loading will be 1 G short of the required aerodynamic force required to maintain level flight.

Should you not understand these basic lift/drag/etc. aerodynamic truths, I certainly agree that you would have absolutely NO IDEA of what I was/am saying.