Why Some Peaks Have Higher Intensity in XRD Pattern?

Every crystalline material exhibits its unique characteristics shape/pattern for identification just like a "fingerprint" for human identification.
Why some peaks in XRD have higher intensity than others?
Using Scherrer equation, the peak width (FWHM) can be link to the crystal/crystallite sizes/ (if and only if, the crystallite size in nanoscale range).
D= κλ/βcosθ
D is the crystallite size (which may be smaller or equal to the grain size) which may be smaller or equal to the particle size; should be in nm
k is constant, dimensionless shape factor depends on the crystallite shape (~0.89 - 1). For homogeneous sample (k = 0.94) and for heterogeneous sample (k = 0.89).
lambda is the wavelength of the incident X-rays (if Cu-Kalpha~0.154 nm or Co -Kalpha ~0.179 nm).
B is the full width at half maximum (FWHM), measured in radian (we have to convert the degree value to radian)
Theta is the diffracted Bragg angle (theta = 50/2 = 25 degree)