Why aurora is only seen in cold places?

The question should be: why are they only seen nearer the Polar regions? The temperature is immaterial.

They result from ionising particles radiating from the Sun, interacting with the Earth's magnetic field. Since the latter can be considered to act as a bar magnet with its poles near the rotation poles, the aurora surround only the magnetic poles hence the planet's high latitudes (North and South).

They are occasionally seen further South, very rarely even as far South as Southern English latitudes, although from there only as a glow in the Northern sky.