I'm sure the airport operators lobbied really hard for this.
No liquid containers over 100 ml means no ability any more to bring interesting drink home from shops in foreign countries, even in sealed containers. But by the most amazing coincidence, the same drink if sold at the grossly overpriced shops in the departure area of the terminal is quite OK.
Now if the regs had said "You cannot bring the drink bottles onto an aircraft", fair enough if that is felt to be a legitimate threat. But that would have screwed the airside retail profits. So it's "you cannot bring the drink through the security point, but can buy as much as you like from the one monopoly supplier, who are our good friends, beyond that point".
Politicians. Don't you just love them.
