Earlier quoted context omitted.
How many sets do you buy per year, out of curiosity? I got into Lego during the pandemic and bought around 50 sets in the past three years. Over that sample, the number of missing pieces was precisely zero.
My experience is in fact the opposite. I usually buy the larger sets, and have nearly always had left over smaller pieces. It made me worried the first time it happened and I spent the time tracing back through the model only to find I didn't miss anything.
I think that’s calculated in their cost of doing business. Add one extra of each 1x1 probably eliminated most of the missing parts issue at a fraction of the cost.