Any reason suggested as to why Pakistan is not actively seeking the return of their citizens?

Were the two men taken prisoner at the same time during the same operation? If so then the question must be asked why a Sunni Muslim was on a Shia pilgrimage? Considering the sectarian violence that was prevalent in Baghdad at the time I could offer a couple of explanations, neither of them innocent.

Return Rahmatullah to where?

The Court of Appeal has got no say in what happens in US Courts (Civil or Military) It has no jurisdiction over any arrest or detention in Iraq, in Afghanistan, or in Pakistan for that matter. It can order the British Authorities to provide what information it has of bearing to the case but that is as far as it can go.

As for revealing identities:

"We are prevented from disclosing their identity and, indeed, the identity of all other detainees, under the Data Protection Act."

The Court of Appeal obviously removed whatever constraints were imposed by the Data Protection Act in this case.

The point of custody has never been brought up because it has never been an issue. Teams of SAS were operating under direct operational control of the US Forces responsible for security in Baghdad anyone they captured or arrested would automatically be under US Military Jurisdiction.