Not of the total electorate almost 30% did not vote passing major constitutional changes on such a small majority is counter to all custom and practice - A local Allotment society would not pass a rule change like this.
Not holding stupid, vague referendums with a mere 50% majority requirement, instead of a supermajority, that can trigger major, complex constitutional changes would be a start.
The rest of the people knew about this vote and they didn't care enough to vote. What are we supposed to do about that? Should we force everybody to vote?
A minority voted to leave the EU.