I think part of the problem is that there is a regime where the atmosphere is too sparse to really act like a fluid or carry away heat. The kinetic energy of th

I think part of the problem is that there is a regime where the atmosphere is too sparse to really act like a fluid or carry away heat. The kinetic energy of the falling object ultimately has to get converted to heat, but the balance between the power delivered to the spacecraft and the power dissipated back to the environment changes significantly with altitude. I think that period of only being able to really dissipate heat by radiation is what motivates the use of insulating tiles. That way the hottest surfaces can be allowed to reach high temperatures without harming the sensitive parts, and the power emitted scales as the temperature to the 4th power, so letting a small part get very hot provides better cooling than spreading that energy evenly out over the whole spacecraft.