That might be true for things like laws, but manners and customs are not strictly enforced by any central authority, at least these days, but rather by how culture/generation changes. It is possible that if nobody follows the same etiquette anymore, it means it is outdated and no longer exists. That is the entire point of progress.

At one point in time, it was considered bad etiquette to interact with people of color, but over time, society changed for the better. That etiquette literally doesn't exist anymore. That doesn't mean people are "getting away with" not following a "rule" these days. But rather customs/morals/etiquette are transitory and prone to changes, and one must understand what is and what isn't actual etiquette instead of just following all outdated "rules".

That's also fundamentally different from something like a law, where the ethical thing to do is that you should still follow it even if others are "getting away" with it.