I think it's similar to decimalisation. People say that this caused "rounding up" of prices but nobody wanted to go back to the old money a decade later. There is simply too much invested in the Euro for a change to be contemplated.
Except that by converting to decimalisation change was contemplated, having had a system in operation that had far more invested in it than the few decades 'invested' in the EU (which of course has changed beyond recognition to the EEC we joined originally). Just because we have invested in something doesn't mean we shouldn't review it periodically, including giving consideration to whether it still meets our needs.