…so it leads to recombination and therefore change of allele frequencies?
With that being said, shouldn’t the circumstance be “no mating at all” to make the law determine frequencies at one specified moment?
Why do you think sexual reproduction should lead to a change in allele frequencies? Each allele is equally likely to be passed down from each parent, and each individual is equally likely— according the HW conditions, at least— to be a parent. What’s the mechanism, do you suppose, by which some alleles would be preferentially inherited? (Spoiler: the whole point of Hardy-Weinberg equilibrium is that there isn’t one.)
The Hardy-Weinberg law assumes random mating and no other factors affecting the frequency of alleles and genotypes in a population. It is a theoretical baseline used to understand the effects of different evolutionary pressures and processes on genetic variation in populations. In reality, populations do not always conform to the assumptions of random mating and no evolutionary forces, but the law still provides a useful framework for analyzing genetic data. So, the frequency of alleles and genotypes can change over time due to a variety of factors, including sexual reproduction, mutation, genetic drift, selection, migration, and more.