Ireland, Denmark and France had referendums because their constitutions required them to do do .
UK citizens did not have to have referendums as its constitution (written and codified ) does not exist .
Parliament has the power to vote for or against major changes to the policies / treaties etc. not the public.
Which raises some interesting points. I think only Ireland
required a referendum before the treaty could be ratified (though I stand to be corrected and in any case it is of no consequence). France voted to accept the treaty by 51.0% (and I don't recall there being howls of disquiet at such a narrow majority). Denmark rejected it by 50.7%. After the defeat Denmark negotiated and received four opt-outs from portions of the treaty:
Economic and Monetary Union, Union Citizenship, Justice and Home Affairs, and Common Defence. The second referendum approved the treaty amended with the opt-outs by 56.7%. I don't think it is arguable that the UK could have secured any significant opt-outs (over and above those it already enjoyed). Mr Cameron tried that before the referendum and failed.
Nobody (well, nobody worth paying attention to) was saying "Ignore the previous referendum, run it again". Ignoring those who voted to remain (and even those who did not vote), there was still an valid argument for a confirmatory referendum - the fact that there was (and still is) disagreement what "Leave the EU" actually meant.
Let's take a little look at one or two of the people who perhaps may be worth listening to (depending on your point of view). First of all, Vince Cable, one time leader of the LibDems, speaking in 2018, just before his resignation as leader:
Sir Vince Cable fluffs a sex joke about the "exotic spresm" of Brexiteers during his keynote speech to the Liberal Democrats' annual autumn conference.
www.businessinsider.com
Theresa May knows that Brexit "can and must be stopped," Liberal Democrat leader Vince Cable declared today, as he called on the prime minister to abandon the "whims of the extremists" in her party and back a second referendum on leaving the European Union.
I remember quite clearly, Mr Cable being among the first politicians I heard commenting after the referendum result was announced: "Oh there's no need to worry too much. We can reverse this." he uttered contemptuously.
Now, the Liberal Democrats in general, at their conference before the 2019 General Election:
Delegates at annual conference agree to revoke article 50 if party wins election
www.theguardian.com
The Liberal Democrats have overwhelmingly approved the party’s plan of going into an election with the promise to revoke Brexit without a referendum, despite warnings from delegates at their annual conference in Bournemouth that it risked alienating some voters.
Under the plan, the Lib Dems would still support a second Brexit referendum with an option of remain, but going into an election would promise to revoke article 50 if the party won an absolute majority – which is seen as highly unlikely.
Now, Keir Starmer, then shadow Brexit Secretary, now Leader of Her Majesty's Opposition:
Labour must not rule out backing a second referendum if it fails to force a general election, Keir Starmer has insisted.
www.politicshome.com
Labour must not rule out backing a second referendum if it fails to force a general election, Keir Starmer has insisted.
There are plenty more where that came from. There were plenty of people (both worth listening to and not) who were dismissive of the referendum result and said variously that it should be set aside, ignored or re-run.
There were people who voted for Brexit who didn't want to leave the CU/SM...
Then they should have voted to remain. As per my earlier post, the two are inextricably linked.
...do they not deserve a chance to be heard?
No. As I mentioned earlier, had the result been reversed there is no chance that disappointed leavers would have been granted a chance to be heard (perhaps by the government negotiating a departure from the SM and/or the CU). So why the other way around?