That sounds like a similar error to reporting US camera sales volume without B&H and Adorama... Not only would you miss a substantial chunk of volume, you'd disproportionately miss higher-end camera sales.
If you look at Amazon's top 100 selling digital cameras, many are point and shoots (including a lot of no-brand specials), the first full-frame camera appears at #37 (A7 III), and there are only 5 full-frame cameras (A7III, EOS 6D II and 5D IV, D850 and A7rIV - plus a couple of upper-end Fujis rounding out the more expensive cameras) on the whole list.
Here's Amazon's #1 selling camera of all (as of Aug. 26, 2019):
AbergBest 21 Mega Pixels 2.7" LCD Rechargeable HD Digital Camera,Video camera Digital Students cameras,Indoor Outdoor for Adult/Seniors/Kids (Black).
Five of the top 10 are cheap point and shoots (two no-names, an Elph, a $118 Sony and a Canon long zoom), plus the latest RX100, a trail camera and three Rebels.
On the same list from B&H, you get 33 full-frame cameras (all of the major models, in different variations), six of which are in the top ten best sellers. The A7rIV is the #1 seller, and the D850 is in the top ten. Neither of those two pricey high-res bodies cracked the top 50 on Amazon.
Another interesting piece of perspective is that no medium-format camera cracked the top 100 on B&H, when there were three versions each of the A7rIII and Z7, plus two versions of the D850 and one of the D810. The A7rIV only showed up once, but at #1 overall. Even the Q2 appeared... Oddly, the best-selling medium format camera was not a GFX (I would have expected the 50R, or maybe the 100) - it was the X1D II at #122.