This is because iron is more reactive than copper in the metal reactivity series.
The metal reactivity series (descending order) : Potassium, sodium, calcium, Magnesium, aluminum, zinc, iron, lead, copper, mercury, silver, platinum, gold
The more reactive an element is, the harder it is to extract it from their ore.
In order to extract iron from iron(ii) oxide, we must heat it with carbon, so that carbon can form carbon dioxide with oxygen, so that iron is extracted. On the other hand, we just need to hear copper oxide in the air in order to extract copper metal.
Because of the difference in extracting the metals, we can know that why iron tools are more difficult to obtain than the copper ones.
