Temperature does not work as you seem to think?
If I were to place an object into water measuring 380 degrees, that object does not heat up because its “hotter” around it. The atoms are 380 degrees, and upon TOUCHING that object, will transfer energy too it until the thermal energy levels up. Heat is just the transfer of energy, its not some magic fire element.
So, in the thermosphere, yes, it does measure 2500 degrees. Thats the measure of the atoms. However, the atoms are spread verrry far apart. Thus, less atoms touch the spaceship less quickly, transferring less thermal energy to the craft. Additionally, its coated in the matieral that Dank talked about, that reflects atoms and mimeses that amount of thermal energy that the atom can transfer to the ship. Heat doesnt just generate more heat. Heat needs to be spread, in the form of energy. Energy is not made, it is transferred from one form to another. Understood?
And please dont reply to this by re-stating about the temperature that metal melts. I already explained why its not melting. If you are going to reply, give me some science.