That seems to have occurred with "ketchup" ...
So I’m not convinced that it’s as simple as all that. I’m not saying marketing doesn’t play a role but it’s definitely not the only thing.
The 'bliss point' might play a major role, amongst various other factors.
60% marketshare in the US rather strongly indicates other people can, in fact, sell ketchup.
> the question is why.
I suspect their continued dominance is a result of marketing plus the effect of expectations of consistency leveraging past dominance.
In the context of evolutionary anthropology this is known as “just-so” stories. Fitting then, that Gladwell’s ketchup essay also contains a just-so stories. He just couldn’t resist.
But they're not perfect, because recently we had ketchup at a restaurant that made their own. It was very, very good, and we preferred it to Heinz. It's clearly possible to do better.
Also, mushroom ketchup is amazing. (Also locally made for that restaurant, apparently.)
To me, there's no more a 'ketchup conundrum' than one for mustard. Until I was an adult, regular yellow mustard was the only real choice. (Yes, there were Grey Poupon commercials. Nobody I knew actually ate it. They did make fun of it, though.)