As with many cases, the law/rules get broken by everyone either intentionally or otherwise.
The point is what are the consequences of a particular breach?
So a Civil servant sends an invite to 100 folk for a BYOB gathering - 70% think "Thats not right is it?" and some question the idea.
30% think "Its in the garden outside the office after work, I`ll pop in".
The person who lives there wonders what all the folk are doing in the garden.
Then somebody "sits on it" and other news for a year and drip feeds the froth machine....................
For comparison, I generally drive within the speed limit however lots of people don`t and some of those get caught. It doesn`t rupture the fabric of society though.