Was something wrong with the basic Sweeney design? to answer this question you have to relate banjo manufacturing in both the USA and the UK.
It would be easy to assume that centres like Chicago and Philadelphia were at the top of the banjo output list, but population reflects demand and at the time, London was twice the size of New York and four times the size of Chicago; Birmingham was the size of Boston and the total population of the USA at 76million was not even double the UK at 46million.
Secondly, density of population significantly affects the consumer's ability to respond to fashions and while the UK only had 2.5% of the landmass of the USA it had 60% of the population and was many years into it's industrial revolution. As a consequence, the UK could respond industrially to any demands placed on it.
Curiously though, banjo manufacturing in London was more influenced by the USA, with regards to style and aesthetics, specifically by SS Stewart rather than by the industrial heartland of Birmingham, a mere 80 miles away from the capital. However it was not long before Windsor, Matthew, Houghton and Riley had industrialised the production of the banjo to meet the overwhelming demand of the fast-developing UK mass market.
Metal was Birmingham’s stock in trade so the zither banjo, with its separately manufactured drum encased in a round wooden sound box (which had the neck attached to it) was the zenith of industrialised banjo manufacturing. The metal and woodworking skills only came together at the time of assembly.
Why manufacture a separate 5th string peg when one could be incorporated, along with the rest in the peg head, and for many years with a spare! But don’t be fooled, there were many beautifully decorated zither banjos made and with the development of a classical style of playing, the more metallic tone was not to its detriment ... and on a historical note it took the German Luftwaffe to finally terminate Zither Banjo manufacturing in Birmingham.
... got to be a banjo joke there somewhere.
Image of Birmingham in the Blitz.