It does seem to be driven by a distinct lack of imagination - even the way it's invariably referred to as foreign 'muck'.
It's not even the fact that some of these holidaymakers hope that there will be some British-style food available in foreign countries, but that they expect it as their right and actually complain if there isn't any!
I think, for many of them, they're so egocentric that they assume British food is standard food and that places abroad that serve non-British food are just doing it to be difficult and to be mean to them.
The same as many assume when people in different countries (or even in Wales, for that matter) 'refuse to' speak English, they're just trying to be awkward or doing it for a laugh.
The very idea that people in a non-English-speaking country might conduct their daily lives in a language that isn't English - or (gasp) not even speak English at all!!