A few hundred years ago, before democracy and the capitalist system, we lived in a political system called "Feudalism". The king was at the top of the heap, then the barons, then the lords, then assorted men-at-arms, freemen, vassals and villeins , and right at the bottom, were the serfs.
A serf's duty was to labour for his lord. He couldn't go work for another lord. He was tied to his locality.
By about 1500, feudalism was gone. People could work wherever they wanted - if one lord was offering poor terms and conditions, yuo could go work for another lord. Obviously, the lords weren't keen on this, but obviously the serfs liked it.
The EU has four freedoms - the free movement of goods, capital, services and people.
The free movement of labour is a fundamental freedom in every civilised country. You won't see restrictions on New Yorkers wishing to move to California.
If we want to have a trading relationship with the EU, they will (among other requirements) insist on the free movement of labour. That's going to be non-negotiable.
The people who thought that by leaving the EU we'd get control over immigration, are going to be just as disappointed by this, as they will be about the fact that in the past, we were not controlling immigration from outside the EU, even though we legally could have.
And, by the way, immigration is the purview of the Home Secretary, who has been Thesesa May since 2010, and clearly didn't carry out David Cameron's pledge to reduce immigration to under 100,000 per year.
Although my feeling is that she's the lesser of two evils.