Scatchard plots are intuitively difficult to grasp because the X-axis is not the "independent variable" of the experimental measurement.
When we do a binding isotherm, we measure B (bound, the dependent variable) at increasing concentrations of free (F, the independent variable). But in the Scatchard plot, F doesn't appear as the x-axis variable, and instead appears in the denominator of the y-axis variable, which is counter-intutitive. So the answer to this question is best explained by thinking about the hyperbolic binding isotherm for the reaction in three segments.
At very low F (below Kd) and very low B, B increases linearly with F. Our calculated B/F is high, and stays roughly constant as F increases. These are the points in the extreme upper left of the Scatchard plot.
As F rises to and passes Kd, larger increases in F are needed to get the same increase in B; the slope of the hyperbola is starting to level off, F is increasing faster than B, so B/F decreases. These are the points in the main part of the Scatchard plot.
At F much greater than Kd, the isotherm approaches and reaches saturation. Large increases in F are needed to produce only small increases in B. F increases much faster than B, so B/F gets even smaller.
Finally, as F theoretically approaches infinity, B reaches Bmax and can increase no further, and B/F approaches zero. These are the points in the lower right of the Scatchard plot, where the x-intercept is Bmax.