It seems Apple is not ending 2017 on a high note. Sales of their latest flagship the iPhone X still have not managed to beat the number of sales the iPhone 6 series has made in 2014.

Consumer Intelligence Research Partners (CIRP) surveyed a sample of iPhone buyers since the iPhone 8, 8 Plus, and iPhone X devices were released in November. The survey ended on Dec. 3. According to Phone Arena, the research firm found out that the figure for the Apple iPhone 8, 8 Plus, and iPhone X sales only accounted for 69 percent of Apple sales in the U.S. To compare, when the iPhone 6 and 6 Plus was released in September 2014, Apple's sale for the devices reached a staggering 91 percent.

This is not the only time that Apple's uptake of newer iPhone models has swindled in the U.S. In the graph released by CIRP, Apple's uptake of newer iPhone models started dropping down to 71 percent in 2015 when the iPhone 6s/6s Plus was released. Twenty-nine percent of Apple buyers chose to buy older models during this time.

Apple's uptake of newer iPhone models rose up to 73 percent, which happened in 2016 when the iPhone 7 and 7 Plus was released. Thirty-one percent of Apple buyers chose to buy older models during this time.

With the release of the iPhone X and iPhone 8/8 Plus, Apple's uptake of the devices was at their lowest. The iPhone X accounted for 30 percent of the sales while the iPhone 8/8 Plus accounted for 39 percent (69 percent total).

The iPhone X's price and availability could be one of the reasons for this phenomenon. The device currently retails for $1,355 for the 256-gigabyte (GB) version on Amazon and $1,099 for the 64 GB version on eBay.

However, Apple's uptake for the iPhone X and 8/8 Plus may still rise up, especially in China where sales have been higher compared to the U.S.