Always when reentering the atmosphere, the shuttle was pitched up, right? When gliding through the mesosphere, how was it that it didn't fly up again then? Was it due to a certain distribution of weight within the orbiter?
Mesosphere stretches roughly from Kármán line (air pressure 0.0000003atm) down to about 50km altitude (air pressure: 0.001 atm) - in technology these amounts of air are typically thought of as "vacuum".
That means even despite the hypersonic speed, the lift generated by such minuscule amounts of air is very low. Additionally, it flew at an excessive angle of attack - about 40 degrees. The effect of that is drag force being roughly the same as the lift force, so the shuttle would rapidly lose speed, and in effect any chance to generate more lift through moving through denser air was lost, as loss of speed was kept at pace with growth of air density.
In short, it never reached air sufficiently dense at speed sufficiently high to produce enough lift to make it rise.