Let us imagine a hypothetical scenario. Two identical shipments are weighted at the same scale during customs. One of them is consistently 0.05% heavier than expected. Then you notice same pattern with a few more shipments. An inquiring mind might wanna open a few boxes and see what is up. *Typoed
Weight is likely taken very seriously by any Customs department due to drug smuggling. And these days, much more malevolent items.
Another good reason for irons, they are a bit heftier than a lot of other small goods, giving less variance from the weight of a small chip.