why cookware does not melt down?
The answer is that cookware transfers the energy from the flame into whatever is being cooked. For instance a pot of boiling water will stay unmelted until all the water has evaporated, after which the pot will start heating up towards the melting point of the metal it is made from.

This is called heat conductance and is used in both cookware and liquid bi-propellant rocket engines (which burn closer to 3000°C). In fact some rocket engines have been made from aluminium with a melting point as low as ~460°C depending on which alloy is used.