Originally Glyphosate was used solely as a weed-killer, and many major industrial crops today have been developed to be Glyphosate tolerant, allowing large doses of the herbicide. However, the idea was that the application was done early in the season and that most of the chemical had decomposed by the time it was harvested for consumption.
However, about a decade ago some genius noticed that if it was applied in a massive dose shortly before harvest it would act as a desiccant, allowing the crops to dry out much more quickly. Farmers refer to this as "pre-harvest treatment". The mechanism is quite simple: the dose is so large that it quickly kills even these Glyphosate resistant plants.
The end result is that not only has the dispensed quantity gone way up, but its late application means that is does not have any time to decompose, and the residual amount left in food products has sky rocketed by orders of magnitude.
Note that trace amounts in certified organic products have also gone up. The popular hypotheses is that this is due to overspray or runoff. These amounts are also typically a fraction of a percent of non-organic.