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?
You know that in crystalline solids we get sharp narrow peaks due to the periodic arrangement of atoms. X-rays diffract only in certain directions. so, at a certain angle, we get high sharp intensity.
A similar answer is for your question.
Some peaks show high-intensity because there is long periodicity in that direction, so at that angle, we get a high peak. if there is short periodicity, for we will get short intense peaks.