Jason Snell, writing for Macworld, on his theory of why iPad sales are falling:

I think the iPad is a victim of its enthusiastic welcome. For a time, iPad sales grew faster than the iPhone, making people believe that the iPad was going to follow the iPhone into the stratosphere as a world-shaking product. We got caught up in the post-PC hype. The iPhone greased the skids for the iPad and made it an easier sell.

As a result, the iPad reached a huge percentage of its target audience in a very short period of time. And once that audience was exhausted, it rapidly shifted into an upgrade-and-replace product cycle. Imagine a world where the iPad didn’t sell 67 million units in the first couple of years, but found its audience more slowly. We might end up with an iPad market just as large as the one we have today, but with a sales chart that looks much healthier.

Part of the reason for that huge wave of early iPad sales was the success of the iPhone before it. The iPhone showed what was possible, but it did so on a tiny screen. The iPad offered that same experience on a (relatively) gigantic screen. Who wouldn’t want that?

With the iPad configured as a media consumption device, I think sales have stalled because we’ve got a “good enough” solution. Not enough has changed to trigger a massive product replacement cycle.

If enough changes in the iPad experience for the masses to embrace the iPad as a content creation device (as Apple is pushing to do with the iPad Pro), I think that product replacement cycle will reignite.