> They went ahead anyway, usually with some tweaks to the language used to describe them but very few substantiative differences.
That's utterly false.
Ireland (twice) got legal guarantees that the scary scenarios evoked by the rejectors, would never happen.
Denmark obtained opt-outs, again listening to concerns and guaranteeing that they would never happen.
France (and basically the Dutch) literally re-negotiated the whole treaty.
Those are substantive changes. I don't know how more substantive you can get than "if we make a law you don't like, you're free to ignore it" and "ok, we'll do it again from scratch".
Now, other member states did hold referendums on these changes, of course - and in some cases, their voting public ended up rejecting those changes. They went ahead anyway, usually with some tweaks to the language used to describe them but very few substantiative differences.