Mainly aerodynamic forces. The heating event is so quick there's not time for the interior of a sizable meteor to warm up. Meteors' thermal conductivity and di

Mainly aerodynamic forces. The heating event is so quick there's not time for the interior of a sizable meteor to warm up. Meteors' thermal conductivity and diffusivity are generally pretty low. Even at 25km altitude, aerodynamic forces are very high and nonuniform with shock wave impingements. These forces will shatter a rocky meteor quite suddenly.