I feel like that is an unreasonable generalization.
It's not remotely hard at all for the FDA to buy products off the shelf and test them for glyphosate. They need not and should not trust samples obtained any other way.
Fair point, it does put some management on to the FDA, but that seems reasonable.. and cost seem small.
Still the FDA can't test all shops, and there is a risk they just test the same shipment. Trusting samples from companies is easy, and fake those samples is a very deliberate crime. It's easy to fake currency, that doesn't mean people do it.
It's not remotely hard at all for the FDA to buy products off the shelf and test them for glyphosate. They need not and should not trust samples obtained any other way.