Because they lock in ancient - 20, 30, 40-year-old - unpublished corporate studies to justify high residue levels on food crops.
Do you recommend washing fruit & vege with lemon water or is there some other way to physically reduce the chemicals on our food?
I do consider that purchasing organic staples - wheat, rice, oats, popcorn - that are consumed in high quantities in Western diets. These are commonly oversprayed with glyphosate during the drying/desiccation process, or permitted to have high tolerances for other reasons that drive high residue levels. I suspect another issue is the fungicide/fumigant/insecticide applied during logistics, that is not discussed much. I try to source local fruits/vegies spray free as much as possible and in season. But most people have to approach this pragmatically due to time and expense and also due to the erosion of cooking skills over the last couple of generations, which creates barriers to getting into the kitchen to do this important but undervalued work. Reducing ultraprocessed foods is a large way to reduce synthetic chemical exposures. The Codex link shows how high the levels of glyphosate that are permitted, other than the staples I mention above. Of course overspraying doesn't involve just glyphosate but other herbicides eg.diquat. A large variety of herbicides - https://eatsafe.nzfsa.govt.nz/web/public/21- are permitted on wheat crops, including dicamba, 2.4-D, metalaxyl, clothianidin... so mixtures are a large but ignored problem. https://www.fao.org/fao-who-codexalimentarius/codex-texts/dbs/pestres/pesticide-detail/en/?p_id=158