To compress a degenerate gas means to change the degenerate particle motions. But that requires A LOT of energy. Pressure only depends on speed of degenerate particles NOT the temperature. To change speed of degenerate particles requires A LOT of energy. Adding heat only causes the non-degenerate particles to move faster, but the degenerate ones supplying the pressure are unaffected.
Electrons are degenerate.
Mass of Sun compressed to size of Earth. Neutrons and protons have room to move around freely. White dwarf cools off from initial formation temperature of about 100,000 K. Form as outer layers of red giant star puff out to make planetary nebula. Compression so great that protons fuse with electrons to form neutrons. Neutrons are degenerate.