The referendum did not become binding when article 50 was triggered. They are separate things.
It has been clear for some time that the UK can retract article 50 and the EU would support that. Remember, a British man responsible for writing article 50 pointed this out a long time ago.
You do not know why "people" voted for Brexit. Different people voted for it for very different reasons. At the moment, financial crooks are getting anxious about EU laws that will come into force a few days after 29 March and will hopefully make their nefarious activities more difficult.
Other people, with almost no experience of any immigration "problem" voted for brexit because life is shit in their part of the UK and they thought they had nothing to lose.
"Brussels" is not elected only in so far as the European Commission is the equivalent of a civil service. Just as the British have powerful and unelected civil servants.
The other institutions are democratically run, either by direct suffrage in European elections or by each country putting forward their head of government or senior politician.
People's ignorance does not mean the EU is undemocratic.
Now "uncontrolled" immigration. The British government has not been interested in controls over immigration from the EU. When the countries of former Eastern Europe joined, the British government chose to welcome them before other countries without any planning for the impact that might have. Other EU countries chose not to do this, as was their right, in order to "control" the situation.
Every other EU country I have lived in also monitor (control?) immigration. The authorities know who I am, where I live, have copies of birth, marriage certificates etc. If I am not self-supporting I can not stay here. My right to stay is tied up with a responsibility to work or support myself. In Belgium, when you move house, the police visit and check you are really living there. T
I have to pay for health insurance. If I don't, I don't have access to health services without paying upfront. There is no accessing medical services without being entitled.
There are plenty of controls to immigration on the EU side. If the British wanted to "control" immigration they could.
But facts are boring aren't they?