Because there are more and more chunks of it that detain me for more little more than a glance. I can rattle through many issues in an hour or less. Their coverage is in those areas too predictable, too reflective of the fashionable media consensus and accordingly less arresting. Their US coverage has always let them down, discreetly parroting the US MSM 'liberal' despair at the irredeemable masses who keep the Republicans in contention.
But as James Allan notes, a similar line and tone is infusing other coverage. Take for example the superior (supercilious) commentary on the recent UK rioting. Nowhere in their comments on the implications for UK politics,and criminal justice, is there a hint of the core insight of Theodore Dalrymple in the Spectator, that all the therapeutic justice prescription in the world is irrelevant while rulers do not understand that criminality is fun. To create and maintain a climate in which such fun is unthinkable, the justice system must ensure that it costs too much to indulge in. Simple really.
For the present the Economist remains indispensable. It is still the best digest I know of events and things worth keeping up with outside my professional sphere of interest. But the less penetrating journalism will make it easy to discard the subscription when my tablet, and the ability to put together my own automatic delivery of best pieces on selected topics from around the world, can fill that need.