Through axles with disk brakes have a few reasons to be. One is the inferred trapping of the axle, and no migration due to reaction forces. Another is repeatable reinstalling the wheel and maintaining the pad/rotor clearances. Well designed through axles control the axle seating into the drop out consistently. Last is with suspension forks there's less flex with a through axle's stiffer axle and larger axle/dropout surface contact area. Andy