Here's why:

* Intense pressure: The immense pressure from the weight of all the layers above the inner core is the primary factor. This pressure is so enormous that it forces the iron and nickel in the inner core to pack tightly together, overcoming the effects of the high temperature.

* High temperature: The inner core is extremely hot, estimated to be around 5,200°C (9,392°F). Normally, this temperature would be well above the melting point of iron and nickel. However, the pressure is so great that it counteracts the tendency for the materials to melt.

Think of it like this: Imagine squeezing a block of ice very, very hard. Even though it's cold, the pressure could cause it to melt and become liquid. The same principle applies to the Earth's inner core.