All the trad bands of the golden era (for that music) of the 1950s and early 1960s had a banjoist, even the star bands of Acker Bilk and Kenny Ball (yes, I know they are sometimes scoffed at as 'commercial' by trad purists, probably because they had more success than the rest, but they were, and IMO still are, very good). I can only assume that on cost grounds the banjoist was the first to go (as perhaps more dispensible than the trumpet, clarinet, trombone, drums, piano and bass) unless anyone knows different? Although primarily a rhythm instrument, you used to get some good solos now and again, and I certainly find there's something missing from the sound without the banjo in the band.