It's the people of the UK that decided the type of democracy that they want. A democracy that also decided on this referendum and the binding power it may or may not have. In Germany, such a question wouldn't be put to the vote of the population. Neither would a simple majority be enough in the congregation of both houses that would be necessary to alter the constitution in such a decisive action. But that is only how we choose to have the country run for us.
What @
GoblinP said is absolutely correct. They chose this. And as sad as it is for the Remainers, that's how even they want their country run. It's their choice. They are free people, free to choose a different Government.