The importance of Afghanistan can be seen from the fact that USA has not forgotten it. Very recently they did a drone attack killing Ayman al-Zawahiri and the air strike was done using air route that passes via Pakistan. USA has complete control over this region via Pakistan and Afghanistan until Taliban took complete control of Kabul.
The last Prime minister of Pakistan did show eyes to USA and other western countries and was quickly removed from power using Pakistan army. Afghanistan is important as it allow USA to sit on borders of China and keep a close eye on Russia also.
Afghanistan is a country, which has a lot strategic significance. But at the same time, for foreign powers it is extremely costly to conquer and hold that country, in terms of manpower and finances.