Tablets still play a large role in retail purchases, as they are the most popular device for sales associates to use to do product demonstrations and often to perform in-aisle checkout. But on the other end of the transaction—the end where shoppers use their own tablets to make e-commerce purchases—the tablet is surrendering many of the purchases it briefly stole from smartphones. That’s according to research recently published from Bizrate Insights.

The iPad specifically has seen a sharp and continual drop in how many purchases it processes, Bizrate said, dropping from control of about 70 percent of such purchases in 2013’s Q3 down to 36 percent in Q116.

“The decrease in the percentage of online sales taking place on a tablet is the result of the increasing utility of smartphones (screen size, website optimization, and improved cell phone coverage), which are nearly always at hand,” said Hayley Silver, a Bizrate VP.

Silver said another reason is the “lack of innovation on tablets that would drive its necessity or improvement for ecommerce” and third is the “lack of a unique identity for tablets. To this last point, retailers often treat the tablet as either the same as the desktop or the same as the smartphone, resulting in a less than optimal experience for the tablet user. Bizrate Insights sees, through its invitations and survey instruments, that tablet users respond best to an experience optimized to their screen versus using the desktop or smartphone experience adjusted for screen size.”

Silver’s points are all quite correct, but there is a more fundamental reason for shoppers using the tablet to make purchases far less often. In short, why do it? As some smartphones have gotten much larger and tablet screens have shrunk, the difference between the pair has shrunk. More importantly, the largest smartphones today—consider the iPhone 6Plus—are still pocket-sized, albeit just barely. The added inconvenience of carrying a tablet just isn’t typically worth it.

The tablets are more often than not replacing desktop devices. Hence, they are suffering from the same loss of device-based purchases that laptops and PCs are. Shoppers are finding more and more uses for their smartphones so they might as well not switch devices. Add to that the fact that there has recently been a sharp improvement in retailers optimizing their sites for smartphone interactions and the demise of the tablet as a shopping tool is hardly a stunner.