What put me off trad jazz was all the dressing up, the waistcoats and bowlers and stripy shirts. And a certain amount of implied racism among the afficionados back in the 70s. It may have started as black music, but I never saw any faces other than pinko-grey in the audience. Perhaps that was a local thing (Coventry then).

As for there being fewer Black people in 1950s Britain, true- but I think irrelevant. There's nothing that says Black people have to relate to jazz- it's an American tradition, and Black British are from West Indian and (mostly West) African backgrounds. In particular, the West Indian connections are well reflected in the development of British music- Calypso, Reggae, Ska etc have all had their place in the rain.