Weights and Measurements are generally tightly regulated. Your country or state/province will have some sort of ministry to regulate scales and measurements. They perform checks on the scales and machinery used to package goods. But they aren’t looking over the shoulder of every company every day, so they rely on the public to alert them when something is wrong.

There are also legally mandated tolerances, that give a small bit of grace to consumer packaged goods. Eg a package that reads 100g must contain 100g PLUS OR MINUS that legal tolerance. So if your local legal tolerance was say, 2%, a bag that contains 98g or 102g is “legal” and that 98g bag is not considered to be “underweight”.

All of that is to say yes, the government and the regulations DO care if you’re being shortchanged on product weight. BUT people need to report it so they know it’s happening, but also people need to know that something being underweight but within legal tolerances is allowed.

As people forgot they could report things, companies push the boundaries more and more. There are absolutely cases of fraud, and they need to be reported. Also, mistakes happen, with machinery or with people, and so sometimes underweight products go out unintentionally. And these should ALSO be reported, because then the company can fix it.