so the reasons for lackluster picture in Islamabad are:-
1) CDA's incompetency and snail's pace movement at developing new sectors
2) Islamabadis having a herd mentality. Everyone jumping on to the band wagon when prices move higher.
3) Lack of real businesses in Islamabad. Most of the residents are salaried people and therefore, have neither the money nor the acumen of the residents of Karachi and Lahore.
As for the first point. CDA not developing the new sectors should go in favor of the existing pool of plots. The market is supply and demand driven. If the supply is low, the prices should move upwards.
I guess there's more to the picture? How about net migration? Did the picture change dramatically over last three years? Are companies moving their HQs out of Islamabad?