Bloke goes into a bar and say "I want a beer and gin and tonic for Mrs Bloke" (who has wandered off to powder her nose)
Simple order you might think
So, would you like Gordons, Henricks, Silent Pool, Slake, Bombay Sapphire, Tanqueray or Beefeaters?
What flavour would you like? violet? raspberry? rhubarb? ginger? unicorn tears (yes its a thing), plain sloe, shiraz
Tonic with that? ? diet? schweppes? fever tree? what flavour?
ice?
lemon ?
Lime?
So you see "Gin and Tonic" isnt simple. Neither is 'Brexit means Brexit because no one knows what that means at all and 'Leave means leave' is just another dollop of rhetoric. No one knows what leave means.
I think your question should be changed from How can the government disobey the instruction of the electorate? to something like how can poiticians lie, deceive, cheat and misrepresent so badly, then dither in circles for three years