That's part of the reason, but the other part is that nobody really likes it as an anthem. Some people get annoyed by 'disrespect', but a non-negligible proportion of them would happily agree that Jerusalem or Land of Hope and Glory or whatever would be a better tune to use instead.
Isn't Land of Hope and Glory a subject of controversy too because of "wider still and wider shall thy bounds be set"?
Also total non-sequitur but I often myself signing Jerusalem as a Christian hymn. I love it.
It is, but a) with our history of imperialism, that's going to apply to pretty much every patriotic song; b) those who'd complain about people not singing the National Anthem wouldn't care about that; and c) 99.9% of the rest of the country wouldn't either - it's the sort of thing that is controversial on Twitter but most of the country are blissfully oblivious of.
That's part of the reason, but the other part is that nobody really likes it as an anthem. Some people get annoyed by 'disrespect', but a non-negligible proportion of them would happily agree that Jerusalem or Land of Hope and Glory or whatever would be a better tune to use instead.
That's a good point that I always forget: the times when its more relevant (sports) its mainly represented England and not Britain and that means that the Scots (and the Welsh) won't treat it like their national anthem and a lot of the English are like "why are we using a British song to represent England?". And then you get the weirdos that seem to think that all four constituent countries should use it because "ITS THE ONLY NATIONAL ANTHEM" but they are a vast, vast minority.
It's even more confusing with rugby, where the Irish team covers both the Republic and Northern Ireland. They sing
Ireland's Call, a song primarily designed to be as non-controversial as possible (mostly it's just repeating the word 'Ireland' vaguely in time to the tune.) Even then, there are always a few Ulster players who don't join in with the singing.