It was more colonialism and part of the Great Game between British and Russia. Lets not forget that Afghanistan had land disputes with Russia along the Amu Darya.British gifted the land to ex indians.
It was to demarcate spheres of influence. If they didn't want to separate the land from Afghanistan then why were the British bombing Waziristan and had 2 aerial campaigns there.here’s a link to a read which includes quotes of durrand himself and the Indian govt in that time. They never wanted to separate the land from afg but read it for yourself.
Following the Durand Agreement in 1893, the British were emboldened in governing the frontier tribes more directly, triggering a massive tribal rebellion in 1897, with the valiant stand of the Yusufzai at the Siege Malakand the most prominent feature. The Afridi also rebelled, even approaching Abdul Rahman, in the spirit of Afghan and Islamic solidarity, for assistance in their jihad. They were blanketly rejected by Abdul Rahman , even as an ‘exodus’ of Afghans traversed the Line to join their brethren in fighting the British. 
^This in it by itself proves that the Afghan historical leadership didn't care, they wanted their piece of the pie.
The British Government will retain in its own hands the control of the Khyber and Michni Passes, which lie between the Peshawar and Jelalabad districts, and of all relations with the independent tribes of the territory directly connected with these passes. For the further support of His Highness the Amir in the recovery and maintenance of his legitimate authority, and in consideration of the efficient fulfillment in their entirety of the engagements stipulated by the foregoing Articles, the British Government agrees to pay to His Highness the Amir and to his successors an annual subsidy of six lakhs of Rupees.The land wasn’t sold, it was Sahibzada Abdul Qayyum who helped mortimer durrand create the agreement. And from the Afghan side it was sayed Abdul latif, both latif and Qayyum knew eachother. Once the agreement was signed, the Afghan king later had Abdul latif killed…
They payed him for the exchange, and the line was ratified by the rulers afterwards. Interesting to note that only when Pakistan movement was gaining steam only then they started to openly oppose.
We've had a lot of sellouts and dawoosan as our leaders. Why do you think we are in this predicament? We are arguably the most disunited ever!logic says abdur rahman couldn’t speak or read English and just went off what someone told him. If Afghans truly sold the land they wouldn’t be fighting over it now. One has to remember Afghans are simple people and follow their old ways. Selling your land/people would be the worst thing to do today let alone back then for a Pashtun.
Technically Pakistan and Afghanistan have been fighting a 70 year long proxy war about it.Borders are not drawn by luck, borders are drawn at the battle field. Until there’s a war, the durrand line issue will exist.
Raazai chi bya kosh wakarho. Ta dakom zaay yay? Za Da Quetta yamI don’t understand your Pashto…