You're missing the point of "the electorate are always right". It's not a moral decision, or an economic one: it's the simple truism that electorates take decisions, and telling them afterwards (or before)
It doesn't mean that the outcomes are right: obviously, there have been bad governments elected in free-ish and fair-ish elections, although not that often (segregationist US states didn't have free and fair elections). It also doesn't mean that individual voters are right, because clearly people that for for openly fascist parties are bad people.
The point is that the electorate, as a whole, judges political positions, and in the UK at least, it's hard to think of an occasion they've got it wrong. If you want to convince them otherwise, convince them. Telling them that they are "wrong" is for losers: you need to make them right. What the slogan means is that it is pointless to go around telling them why they don't understand, and if only they did understand, they would do differently (the Tories under Howard, who sought an apology for 1997; Labour under Miliband, who were still fighting 2010, if not 2005). You need to convince them that you are right.
Labour were deaf in 1979 and 1983. It took until 1987 for Labour to get even close to starting to talk with the electorate. The Tories ditto in 1997 and subsequently until 2010 (and even then they weren't great). For as long as parties believe that they were right, and it's the electorate's fault they lost, they continue to lose.
And you can point to quite a number of other "surprising" results and see that the electorate were ahead of the politicians: 1945? Yes, Winston, great wartime leader, thanks, but no thanks. 1950? The NHS is great, thanks, but bread rationing like we didn't even have in the war? No thanks. And so on.
Parties that don't listen don't win. Remain didn't listen. Remain stood on the moral high ground and shouted.