Why aren't there more precise, individualized recommendations based on genotype for each SNP?

Research that looks at more specific interactions between SNPs and factors like Vitamin E intake, air pollution, exercise or composition of dietary fats is still not that common and tends to be under-powered. One piece of research may appear to settle the question, e.g., a SNP may offer protection against asthma from ozone exposure. But dig a little deeper and one finds results in another study that found the exact opposite, or no association at all. In the early days of personalized genomics, researchers felt optimistic about the quick development of tools for individualized advice. However, in many areas, concrete advice based on genotype has been elusive and more work needs to be done to unravel all the complicated interactions of human biochemistry with the environment. This 2018 paper on precision medicine (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6316334/) and Vitamin E dosing says it well, "The core information that exists at present is insufficient to deliver precise recommendations."