Why are the results of genetic crosses shown in punnett squares interpreted as probabilities, not certainties? give some specific reasons?

I believe this is because the types of offspring produced by any genetic crosses depends on chance such that there is no certainty of getting a particular trait. For instance, the number of gametes produced that contain particular alleles depends on chance and it is not certain. Likewise, the fusion of two gametes with particular alleles is not certain. Therefore, the outcomes of genetic crosses shown in Punnet squares are just probable or possible outcomes.