What Drove Shahzad to Terrorism?

Liberal commentators suggest that mortgage foreclosure on his Connecticut home led Faisal Shahzad to pack an SUV filled with bomb-like materials and attempt to take many innocent lives in Times Square. While other liberal outlets won't ascribe a motive to the terrorist --instead, they say, "Motive Still A Mystery" --who previously spent months in Pakistan, probably training for the big day. But the New York Post doesn't buy such ludicrous claims.

Instead, the Post says:  

Admitted terrorist Faisal Shahzad -- who copped to training in explosives in the past year with Tehrik-i-Taliban Pakistan, the leading extremist Islamic group in his native Pakistan -- said he was driven to evil by the slew of deaths among leaders of the terror group, law-enforcement sources revealed yesterday. His training came in a tribal area where American drone aircraft have pummeled members of the Pakistan Taliban and al Qaeda in the past year. Sources said he was an eyewitness to the onslaught throughout the eight months he spent in Pakistan beginning last summer. The Pakistani Taliban claimed responsibility for the Times Square bombing attempt immediately after it occurred, saying it was in response to the drone killing of one of its leaders in August -- but that claim had been roundly discounted by US authorities at the time.

This sounds like a more plausible motive for Shahzad. So why aren't liberals inclined to discuss this?