This isn't surprising. The first few weeks of January usually have the weakest sales, as there is usually little to no new music being released (major labels avoid it for releases), and the retail sector usually struggles in January. This is just a continuation of the trend of declining record sales.
I thought this was in reference to first week sales and I my mind was about to be blown. Impressive she holds the number one spot still months after this was released, despite the fact that sales are so low.