> Is there some sort of cultural blind spot which prevents them from understanding that there are better ways to do things?

Yes, but it's not specifically British: most nations (and many companies) I've looked at in any depth seem to have this blind spot — "not invented here" is one of several kinds of in-group favoritism.

https://en.wikipedia.org/wiki/In-group_favoritism

Also see this with diets, religious and political affiliations, and back in the day used to see it with Mac vs. PC.